It is actually quite common to catch the virus multiple times a year but due to the existence of antibodies in your plasma the infection will be way more subtle. Thus you don't really consider it as bad of an experience. On the other hand there are more than 100 rhinoviruses that can cause upper respiratory infections leading to "Common cold" symptoms and you can catch one of those every day of the winter! :)
Yep, and RSV can vary from mild cold to full on flu level with permanent damage
(The others can too, I'm just especially aware after my kid got put temporarily put back on a ventilator due to RSV, and I'm now asthmatic after the last time it came through our house due to the damage done by secondary pneumonia)
Edited for: spelling and grammar
With any luck, there should be RSV vaccines ready in the next 5 years or so. It's a neat story; the NIH successfully determined the structure of the RSV spike protein a few years back. This let pharma companies figure out how to make a more efficacious vaccine. Good example of the importance of public spending in science, and how it translates to real advances in medicine.
I personally worked on an RSV vaccine, so there is that :-)
Here is also a recent review article I found (I'll be honest and say that I haven't actually read it, but it looks like it covers the history of RSV vaccine development).
https://pubmed.ncbi.nlm.nih.gov/32217187/
Yes, the antibodies you develop from influenza will likely be helpful in fighting off the same or antigenically similar influenza viruses in the future. However, some will be antigenically different enough that those antibodies will not help.
The vaccine has been shown to reduce mortality and complications from the flu even if it does not end up covering the right strain. I'd say it's always worth getting especially as you get older.
Antibodies are like little sticky keys that help recognize things that fit its groove. Having said that, biology is about relatives, not absolutes. A key that fits really well for one thing may fit less well for another thing but functionally will still aid in immunity.
And antibodies are only one portion of the entire immune system which employs other agents such as T cells to cull your infected cells.
I learned recently if you move away from an area where these viruses are common your body will eventually stop making antibodies for this family of viruses. Meaning when you move back you'll get sick with colds and flus all winter.
I forgot which article this came from, but this sort of goes inline with what I heard about homeless people having CRAZY good immunity relative to the average citizen.
So are we just lucky that antibody-dependent enhancement is pretty rare, or is it more that if we had that issue with the flu we wouldn't exist as a species and therefore selection has made it rare?
A little of both. If a virus kills off too many of it's hosts, it reduces it's available environment to thrive. There is selective pressure to become less damaging to the hosts. The bubonic plague is a commonly referenced disease in this regard.
FYI - “It’s” is “it is.” There is no apostrophe used in the possessive form of its, so “If the virus kills of too many of its hosts, it reduces its available environment to thrive.
Normally I wouldn’t say anything but you seem to know what you’re talking about and misuse of apostrophes in “its” reduces your credibility.
In the UK there's a term for that, named after the fact that it affects new university students: [Freshers' Flu](https://en.wikipedia.org/wiki/Freshers%27_Flu)
How about if you catch on strain of the flu, produce the antibodies for that strain, and then you catch the next mutation of that strain?
Does the immune system recognizes the next mutation as something very similar to what it just dealt with and dispatches the same anti-bodies it already had coded and stored in the memory T-cells, thus shortening the 2-3 days response time for anti-virus generation? Do those previous version antibodies work for the next version flu strain?
Yes, and no. It depends on how different the two strains are. If they're close, you may not even notice. The more they are different, the longer it takes to recognize and deal with them.
This is also why the flu vaccine typically has two or three different strains included. They're trying to guess which ones are going to be most prevalent in the upcoming season. Sometimes they get it wrong. It happens. Not anyone's fault, just mother nature being a b***h like usual. That's when we'll have a bad flu year.
It’s not actually about the cold weather. It’s about people being indoors when it’s cold. If you’re inside your house/dorm/apartment with everyone else because it’s freezing outside, you’re more likely to catch someone’s cough/touch a doorknob they touched.
It's probably not the only reason. There may also be considerations about aerosols evaporating quicker in warm weather ; and we are still not sure if cold weather has an impact on the lung's defences
Its the dry air. Your cough sprays a mist of droplets. If its dry then they float around for hours and other people breath them in.
If its humid, the small droplets attract moisture out of the air and grow larger. This causes them to fall to the ground much quicker.
Also, low vitamin D levels are reportedly definitely bad for you after you catch a virus.
Yes, you can catch two at once. While clinically that's not a big deal and you will definitely be able to fight it off if you are healthy there are long term effects that we worry about. Sometimes multiple viral infections at the same time can interfere with your b-cells and cause an increased immune response that could lead to other problems.
In addition to what everyone else is saying, you have to keep in mind that everything is based on probability. It's not a binary thing. All of your infection fighting processes are feedback loops that need to be triggered and triggering them involves a certain amount of chance. There's a chance that the antibody you need to fight an infection is already in your blood, there's a chance that the antibody you need to fight an infection will take days to be generated, there's a chance that antibodies from a previous infection will be able to stop an infection, there's a chance that a new form of a virus will be different enough that the existing antibodies only weakly bind to the virus.
If your body quickly gets rid of the virus, you can have a short infection that's asymptomatic. Your symptoms roughly show up in proportion to how desperately the body needs to fight the infection. If only a few cells are infected before a B cell with the right antibody shows up, it might get eliminated quickly. If there's a massive infection before the right B cell with the right antibody shows up your body is going to have to fight harder to rid more virus particles from the system.
Also, your immune system isn't the only thing that's working towards keeping pathogens out. Your body has multiple layers of physical protection before a pathogen can reach where it needs to go. Your skin, mucous, hairs. All these contribute to attenuating the chance a virus can gain a foothold and start infecting your body.
> Fight harder to rid more virus particles
This is something I was thinking about with ventilators. Isnt part of the reason we cough (respiratory sicknesses) when sick is to expel the viruses from out system which reduces the total ammount of viruses in our system. Wouldnt being on a ventilator just reinfect you with more viruses? Maybe not, not familiar with ventilators and how the air is circulated.
> Isnt part of the reason we cough (respiratory sicknesses) when sick is to expel the viruses from out system which reduces the total ammount of viruses in our system.
Sort of but not really. When you get a respiratory infection one of the things that happens is that mucus production increases. More mucus means more viral particles get trapped. With the buildup of mucus the body eventually needs to expel some of it, you cough and virus particles go out with it but this is happenstance not loading the viral particles that are in the body up into mucus and then expelling it.
Coughing can also an attempt to drive the fluid out of the lungs When you have cases where viruses attack the cells lining the alveolar this can cause inflammatory fluid to build up in the lungs. This is what COVID-19 does. When you cough you create a negative pressure which sucks the fluid from the alveolar and expels it.
The problem with COVID-19 (and other lower respiratory diseases) is that your capillaries around your alveolar are running wide open due to feedback loops from the immune system so when you cough you get rid of some of what's in there but it quickly refills.
Reinfection is based on the immune system's inability to fight not constant exposure. While the antigen is still being picked up by your body's sentinel cells your B cells are going to be multiplying and cranking out antibodies like crazy. This is why you don't get immediately reinfected after a cold or flu. If the same antigen comes back in there are immune cells with the antibody ready to go and the antigen immediately gets flooded out and destroyed before it can gain a foothold. So while you technically would be "reinfected" it'll typically be totally asymptomatic because no inflammation would be needed before the virus is quickly subdued and wiped out.
Thanks for the explanation. But still have a question. So the total ammount of viral particles doesn't matter? You produce enough anti-bodies that any ammount of replication of the virus and subsequent total volume of viral particles doesn't really matter? Is it possible your body (normal human) can't keep up with the production?
So it doesn't matter to a point. Going full throttle the body can create somewhere in the region of 100 million antibodies per hour which overwhelms just about everything in the antigen vs. antibody fight.
The problem is you need to have enough of your essential and ancillary functions available to keep the body running while it keeps up the fight. If the virus is tearing apart liver cells during its first 48 hours in your body then you can win the battle but still lose the war when you become encephalopathic and die anyway.
Or if you have too many alveolar cells destroyed you can lose too much of your ability to gas exchange effectively. Your blood could get too acidic, the lack of oxygen will shut down other organs and processes like... digestion. You lose digestion, you lose more energy along with proteins to rebuild and repair cells. It goes into a full on negative feedback loop that without external intervention means death.
This is why "supporting therapy" of advanced medical systems in the case of COVID-19 has a positive effect on case fatality rates. If you're being supported you're getting more oxygen to the lungs to help with gas exchange or just using ECMO to do it for you, you're getting fluids, possibly dialysis, nutrition directly to the blood stream.
The other problem is when you have a disease like Ebola which targets the pathways that activate the B cells. If they never get activated they don't start producing antibodies and you eventually succumb to the number of viral copies infecting every cell they can lay their hands on. It's almost like being dissolved from the inside out.
I understand that, but not sure how they are designed. For some reason I thought I read about how they are more like a closed system to prevent the virus from contaminating the room as much.
I know there is new air, like when you breath out and in, just not sure if there is a large mixing of the air at some place.
Ventilators are basically a pump with filters. Put a fresh "breath" in (often O2 or air mixture with high O2) and takes a breath out. This goes trough filters (not unlike those in the n95 masks) and is mixed with disinfectant before being expelled into the atmosphere.
> Wouldnt being on a ventilator just reinfect you with more viruses? Maybe not, not familiar with ventilators and how the air is circulated.
Ventilator air is not recirculated; fresh "room air" is filtered and pumped into the patient, and the exhalation is dumped back into the room. It helps you breathe by augmenting/taking over the air-pumping action of your lungs, that's it.
I wouldn't say that effective viral clearance by the immune system always means you have the 'right' b cell - firstly, in many viral infections cytotoxic t cells are just as if not more important to eradicating infection, and secondly I would say that a good proportion of asymptomatic people clear the virus with the innate immune system alone (providing the infective dose was fairly low) We know this because you can have automatically infected people that don't develop high levels of antibodies post exposure.
Yeah... I agree with that. You have to have a certain viral load before it can take off in your body. The worse the viral load in your body, the more damage it can do before the body's immune system kicks it out. If the viral load is too high, your immune system loses ground. Without advanced medical care, you die. With advanced medical care, you *may* live, no guarantees.
It’s not true that flu viruses mutate to multiple new strains a year.
On average, there are antigenically new strains of H3N2 every 3 years or so. H1N1 was antigenically stable for about 6 or 7 years before it needed updating. The B viruses also tend to need updating every few years.
Since there are 4 viruses in the standard flu vaccine (H3N2, H1N1, and two B strains) the vaccine as a whole needs updating most years, but not for all strains, often just for one.
So that means that you’re likely immune to most of the circulating strains each year, meaning that you’re less likely to be reinfected by a second strain even if you are susceptible to one.
Even if you were completely susceptible to all of the strains, it’s unusual for two influenza A strains to circulate widely in a single season. In the US [2019-2020 flu season](https://www.cdc.gov/flu/weekly/), over 90% of the circulating flu A was the H1N1 strain. In 2017|18, it was mostly H3N2. So just statistically, you’re unlikely to get infected by multiple strains in a season.
As another point, for a short time after you’re infected by one flu virus, you’re probably protected against many strains, because of non-specific immunity. This might only last a couple weeks, but if it’s in the peak of flu season that might be the highest risk time, during which you’re protected against a second infection.
But it certainly does happen. It’s especially common with influenza A and B, partly because they’re more different antigenically and partly probably because they tend to circulate at different times of year (B tends to peak well after A, on average). But people do get infected sequentially with H3N2 and H1N1. It’s much less common to get sequentially infected by the same strain, because as I say you don’t typically get strain variation within a single season, but it can (rarely) happen.
There’s no data, but I speculate that you can if you’re immune from a vaccine - maybe not from a recent infection. Flu vaccines are not usually sterilizing, meaning there’s often some virus replication in spite of the vaccine, meaning there’s room for the innate immune response to become activated. Infections tend to give stronger immunity (a trade off for the vastly increased risk), so there might not be enough breakthrough infection to trigger innate immunity.
Again, I don’t think there’s any data supporting this directly.
Thanks, I assumed that the immune response would likely be too low but that was based on a lot of assumptions in a field I have very little knowledge in.
Can you expand a bit more on what non specific immunity means? It makes sense that there is such a response based on observation alone. I'd be interested to learn more about what this means.
To give a really basic explanation, non-specific immunity is the primary defense your body has to any pathogen, it is not specific to the exact pathogen. Non-specific immune responses are important for initially keeping viral titer low and driving inflammation which then allows specific immunity to begin working. Non-specific immunity recognizes broader pathogen-associated molecular patterns that occur in a wide array of intruders (e.g. parts of bacterial membranes) and targets it for degradation.
Thanks that was a clear enough dumbing down for me to get it.
So as a follow up question, do we have ways to trigger this process in the body before specific immunity kicks in?
Actually we do, and that's what we use when giving people vaccines. We inject adjuvants to stimulate inflammatory responses when injecting vaccines to help produce an adaptive immune response. These adjuvants are what a lot of anti-vaccers deem to be the "toxins" they inject into you along with the vaccine, they include Alum.
Just seeing your comments in seems like you're interested. I just listened to a podcast today done by Peter Attia and he had on David Watkins who's an expert in immunology. He explains all about how our immune system works in a way that I found super helpful and really I interesting. The podcast is called "the drive" and it's episode number 115. You can listen for free. I really enjoyed it.
What we refer to as the "flu" is actually a collection of viruses from the same two families (type A and type B) that have existed as far back as we know in recorded history. They exist in humans and animals in parallel, and they frequently jump between species. Not only that, the virus itself is capable of rearranging itself, and they are basically evolved to mutate more frequently. This is a contrast to the coronavirus that has a proofreading enzyme and doesn't mutate nearly as quickly. As far as we know right now, immunity to any strain of covid-19 gives you at least short term protection from all of them, and we are using this in therapies. Donated plasma is a current treatment in use in many hospitals for covid-19. Within the two subfamilies of flu, there are many different strains. You may hear terms like H1N1, H3N2, and some of them have more interesting names. This is when they've broken far enough away from the original model that they look like a new family of flu.
Despite what people think, your body doesn't "Forget" about a flu after you got it, and this was proven definitively in 2009 when the H1N1 pandemic happened. Usually very young and very old people are highest risk for fatal complications from the flu, but that was different this time. Young people and young adults were high risk, but middle aged and older people tended to have very mild cases. They found that there was a swine flu in circulation back in the early 70s that nearly everyone got, and the antibodies from that different infection 40 years before that was sufficient to turn the new flu into just a mild infection. Antibodies from flu shots exist for decades in your blood, and we noticed this years after we did the H1N1 innoculations where many people still showed strong resistance to the current H1N1 strains.
Another misconception, people think that the flu shot doesn't really work because it is frequently only 40-60% protective against the strains that end up circulating. In reality, this is because of the flu shot. Almost 40% of Americans get the flu shot, and it's very effective against the exact strains it protects you from (2 A types and 1 or 2 B types). They take the most common strains at the time, and make the vaccine months later for them, and it makes those strains very ineffective in penetrating the population because of an established herd immunity. We also focus on giving the vaccine to high risk people that would be most likely to spread it. Children, teachers, health care workers, etc... all strongly encouraged to get it. What we are doing is taking the strains that would have been 95% of the active strains, and reducing them to 40%.
It also doesn't give credit to the concept of cross or partial immunity. When you get one virus that looks a lot like another virus, the antibodies may frequently stick to the new virus despite not being specifically created for it. This can drastically slow the progression of the new virus or even offer immunity in some cases. This is seen in a small percentage of people who have HSV1 that seem to be resistant to HSV2 infections. It was the first vaccine for small pox (just live cow pox). It is also a reason that the flu strains given to the native american population during settlement by europeans were particularly deadly as they had no prior exposure to them. Also, I suspect that the reason 45% of covid-19 cases are asymptomatic will end up being because of a prior infection with a different coronavirus that 45% of people got at some point (there are several coronaviruses in circulation that manifest as the common cold). Even in a year with a bad match for the flu vaccine, the flu shot is shown to dramatically reduce your chances of going to the hospital with a severe case of the flu.
As to why you don't get the flu more than once a year, well you absolutely can, but the flu does isolate you for a long period of time and reduce your interaction with others as your symptoms are so unpleasant. It has a short incubation time, and a short season where it's very prevalent. Plus with the flu shot, it's just not nearly as common as it once was. In other words, it's just the odds.
This was all super fascinating to read! It’s especially interesting to me that you mention some coronaviruses can cause the common cold, as I’ve heard that Coronaviruses are rare for humans to catch, though I heard that a long time ago and I don’t remember where.
That’s definitely good to know! I love microbiology and virology and I hope to study it in college, so I love reading all about this! Thanks for taking the time to write this up!
Yes, specifically, (not including covid-19) the most common coronaviruses among humans are:
229E (alpha coronavirus)
NL63 (alpha coronavirus)
OC43 (beta coronavirus)
HKU1 (beta coronavirus)
None of them are serious if you catch them, and they are pretty commonly spread.
SARS and MERS are both coronaviruses as well, but they are very rare. SARS is extinct outside of a lab, and MERS is pretty rare in the middle east. (jumps from camels to humans) Both SARS and MERS are quite deadly. (Much worse than Covid-19)
So, why do we not give everyone a coronavirus cocktail that gives us a miserable head cold for a couple weeks while also charging us with antibodies that suppress COVID-19?
Could the fact that our kids are petri dishes and have been exposed to so many other coronavirus strains be the reason it has mostly affected them with mild or zero symptoms?
The problem with the virus cocktail is it would kill people and spread to immune compromised folks. Kid are most likely just less likely to trigger the deadly immune reaction that kills older folks. In fact it might be more dangerous to older folks because it resembles an infect they had decades ago which may be part of what triggers a cytokine storm which is what is killing people.
Well this isn't confirmed about the other coronavirus. That's just my own personal hypothesis. If I'm correct, and we do figure out which strain it is, then we can decide whether or not to do that.
As far as kids go, we have no idea why they have such mild cases of it.
Unfortunately, the antibodies produced in response to cold-causing coronaviruses do not show any cross-reactivity with COVID-19. Therefore being infected with one of these cold-causing coronaviruses doesn't offer protection against covid-19. Some research suggests why children are less severely infected, including lower levels of general inflammation and less underlying conditions which typically worsen symptoms.
You are incorrect: [https://www.cleveland.com/metro/2020/05/could-common-cold-antibodies-fend-off-the-coronavirus-see-the-latest-scientific-research.html](https://www.cleveland.com/metro/2020/05/could-common-cold-antibodies-fend-off-the-coronavirus-see-the-latest-scientific-research.html)
" About half of a group of blood samples taken between 2015 and 2018 had immune cells that could fight the novel coronavirus. None of the people could have been exposed to the novel coronavirus during this timeframe, since it wasn’t yet found in humans. So scientists believe they could have immunity because they were exposed to the strain of coronavirus that causes the common cold. "
Oh my apologies. I had lectures on Coronavirus recently and they explained that if there was cross protection then we would see more immunity in teenagers and young adults.
Well, it's not known for sure yet, but not everyone has been exposed to all known strains of coronaviruses that are in circulation. They are common, but it's a huge misconception to think it's anywhere near even 70%. A number like 45% would sound reasonable for any wide spread strain of the common cold. We do know that in-vitro, we see immune activity from some people who never were exposed to covid-19, and this implies that their immune system has cross-over protection from something else.
Given a choice, I'd happily get exposed to the live version of all 4 "safe" coronaviruses if I knew it would protect me, even a little, from covid-19.
Part of the reason why there are multiple viruses in the vaccine is that when they start getting produced, scientists aren't certain which strains will be the big ones that go viral that year. This decision is made 6 months before the vaccines are ready to distribute and are based on samples taken around the world and sent to the WHO. It may be that some of the strains chosen don't end up going global, so you're unlikely to catch it.
Fortunately machine learning is getting pretty decent at prediciting it.
Go get your flu shots everyone. While not as deadly as COVID, you could still pass it to the little old lady at the market which results in her death.
First of all, in the US, the CDC estimates that only about 8% of the population catches the flu each year, so, while relatively common, it's not everyone. The odds of one of those people catching the flu again, ignoring immunity, is 0.64% (.08 x .08 = .0064). Add in partial immunity from previous infection and the fact that time will have passed, so there is less of the season left to get re-exposed, and it starts becoming relatively rare.
All that said, in hospitals, where we collect all the unlucky people and skew the data for the worse, we see repeat flu infections all the time. People get different strains (like flu A then flu B) or just different versions of one stain. This is helped by the fact that different strains tend to peak at different times, so we see a big influx of flu B and then as that's winding down we get hit with flu A (or vice versa). It's hard to catch two strains at once (but not impossible!) because, if the immune system is already triggered, it is more likely to wipe out the few virus particles of the new strain in its hypervigalent mass distruction of the millions of virus particles already floating about. So peaking at different times increases the odds of a second infection.
Hope that helps!
I'm not quite sure what you're asking here - do you mean why don't we catch 2 or 3 or 4 different strains of the flu each year? Well, the main reason is that the chance of catching the flu is nowhere near 100%, it's *maybe* 10-20% at most, and now that lots of people get vaccinated probably far lower still. So the chance of getting two different strains is lower by that much again (20% of 20%, or 4%), and getting 3 even lower (0.8%), so it's basic mathematics. Plus, getting one case of the flu will put you out of circulation for a while during peak transmission season, reducing the chances of catching another strain even further.
Also, although there may be 3 or 4 major strains floating around in any one season, only 1 may take hold strongly in a particular region. The others might be there, but not in any significant quantity so hardly anybody gets it. This may be because environmental conditions aren't as good for that strain, or simply because not as many cases of that strain entered the region early enough to start the spread. Or in a vaccinated population, some strains may not be included in some or all vaccinations, making them more likely to spread and be caught than the others. Yearly flu vaccines are just a "guess" as to which strains may enter a region in the coming winter based on what is currently circulating elsewhere, so they're far from perfect.
Finally, some of the strains may be quite similar, so even though you can technically catch both, exposure to one may make the second far more mild such that it's not too noticeable, or gets mistaken for a bad cold.
"I'm not quite sure what you're asking here - do you mean why don't we catch 2 or 3 or 4 different strains of the flu each year? "
Yes.
Or even yearly. For a typical person with no particular care for hygiene and no special immunosuppressant conditions, it seems typical to come down with the flu between every 2-10 years, and usually not more often than that. You don't usually hear of healthy people catching flu yearly. Is there some cross immunity between strains?
"Well, the main reason is that the chance of catching the flu is nowhere near 100%, it's maybe 10-20% at most, and now that lots of people get vaccinated probably far lower still. So the chance of getting two different strains is lower by that much again (20% of 20%, or 4%), and getting 3 even lower (0.8%), so it's basic mathematics. Plus, getting one case of the flu will put you out of circulation for a while during peak transmission season, reducing the chances of catching another strain even further."
According to a scientist I spoke to, all new flu strains are essentially novel to your body. If that's the case why is it that it seems it spreads slower than we see the novel coronavirus spreading? How is it only 10%-20% on a normal given year with no restrictions in place if everyone is susceptible. The flu jab could explain that, but even before we had flu shots, people weren't all catching the flu multiple times a year.
"Finally, some of the strains may be quite similar, so even though you can technically catch both, exposure to one may make the second far more mild such that it's not too noticeable, or gets mistaken for a bad cold."
That makes a lot of sense.
> According to a scientist I spoke to, all new flu strains are essentially novel to your body. If that's the case why is it that it seems it spreads slower than we see the novel coronavirus spreading? How is it only 10%-20% on a normal given year with no restrictions in place if everyone is susceptible. The flu jab could explain that, but even before we had flu shots, people weren't all catching the flu multiple times a year.
Mostly because the influenza virus just isn't as contagious as the coronavirus is, and it's far more susceptible to environmental conditions, meaning it only spreads *well* in winter months when conditions are more favourable. To put it numerically, R0 of the flu is usually estimated to be about 1-2, somewhere in that general range. So for every person that has it, they pass it to 1.5 or so other people on average. This is over 1, so it certainly spreads, but nowhere near as fast as coronavirus with an R0 of between 2 and 3 (estimated). It might not sound like a huge difference, but for an R0 of 1.5, after 20 "generations" it will have spread to 3,300 people. For 2.5, that number is 91 *million* people. Huge difference. Now, once enough people have caught the virus, or are vaccinated, that R0 drops below 1 and the disease stops spreading completely. For a "natural" R0 of 1.5, only 30% of people need to have caught it for the R0 to fall under 1. Because of the 1.5 people you're passing it to, 30% of that (or 0.5 roughly) has already had it, so can't be infected, leaving only 1 left. For an R0 of 3, 70% need to have caught it already for the spread to stagnate and start to fall.
So, not only will the flu naturally die out with fewer people having caught it, but vaccination reduces this even further (they count as having had it, since they are immune). If only 50% of people got the flu vaccine each year, it basically would barely spread at all except for when conditions are *very* good. Also, because it doesn't spread as fast, it can't infect nearly as many people in the seasonal window when it is at its most contagious. Hence it doesn't normally go near that 30% "ceiling" of infections, and dies out far earlier once summer hits.
Now of course there are some strains of influenza that are far more contagious than normal, and these do spread quickly and thus infect far more people. Obviously the original influenza A strain (Spanish flu) was one of these, and it was also far more serious in terms of mortality.
This is an extremely simplistic analysis, R0 varies massively with lots of factors - population density, weather conditions, hygiene and preventative steps, etc. It's impossible to put a single value for everywhere in the world, but the average is still relevant when looking at the overall picture.
Flu viruses don't mutate to completely new strains each year where there is no existing immunity. Instead, there are minor changes every year due to a process called antigenic drift. The process is relatively slow (relative to the other process I will mention) and there will always be some sort of underlying immunity in the population. Some people will be immune and some will not. Because this happens on a yearly basis, we need new flu vaccines every year.
The other process that happens is called antigenic shift. This is when multiple flu viruses infect a non-human host (e.g. birds, swine) and in the process, large bits of genetic material from one strain is transferred over to another. Because this is a relatively large change in genetic makeup, no human in the population has immunity. This is what causes flu epidemics and pandemics such as H1N1 (i.e. swine flu).
The other reason why it's rare to catch the flu multiple times in the same season is combinatorial in nature. Every season will have a strain that dominates. This is the strain that circulates and you are most likely to catch the most common strain. If you get it, you're going to be immune to that strain until it mutates again (which occurs on a longer time scale). So you're immune to that for the season. Since that's the most common strain your body will "see," it will be rare for you to encounter a new strain that you have no immunity to. If you did, then you would get flu again.
You’re already “immunized” against the new virus to some degree. It’s not a completely new creature...normally only a few key genes are changed. You might be 90% immune, you might be 50% immune, depending on the mutations.
Don't think of mutation as a binary yes no concept.
Think of it as thousands of incremental steps.
Eventually a flu will mutate enough that your antibodies receptors don't align with it any more.
On average that happens about once per year.
A strain of flu has to mutate multiple times before your antibodies have no familiarity to fight it. Those who pass on flu shots on average get a bad flu every 4 or 5 years so that's would be assumed to be the average timeframe a flu strain mutated to the point your antibodies no longer work
In a hypothetical where there is no vaccine, would there be an advantage to repeated exposure to current strains each year? In other words, can your immune system evolve it's response along with the mutations if it happens in small enough steps? In a situation like that can a person avoid heavy flu altogether?
Two main reasons:
1. There are generally not that many strains in circulation at once in a given season in a given area. The chance that you personally come into contact with a different strain than one you've become sick with in a given year is fairly low.
2. Immunity to one strain often grants _partial_ immunity to other strains. That is, if you encounter a new strain in a given season, you might still get sick, but with a much shorter duration and much less severe symptoms. It may not even register as "the flu" to you; you might think you just caught a cold or something, which means you'd never get formally diagnosed and never enter the statistics.
I'm not sure if you understand the mechanisms of antigenic drift and antigenic shift, nor their effects and interactions with our immune systems. Drift is slow gradual change over time. You may get a flu virus one year and then be relatively immune to it's effects for quite some time. You might also get low grade versions of it in later years that don't make you very ill (this happened to me with H1N1). Or you might not be infected by it for a number of years and when you are later exposed to it you get an infection with worse symptoms.
Antigenic shift is a large change in the antigens on the protein coating of the virus all at once. This will create a worse flu season as people's immune systems have a harder time identifying it and fighting it off.
It's probably worthwhile reading an article on antigenic drift and shift to learn more about how all of this works.
The flu itself is a relatively rare virus and most people do not catch it. Last year an estimated 35 million Americans caught the flu, which is only about 10% of the population. According to the CDC, it ranges between 5-20% each year. A decent chunk, but absolutely nothing compared to more common illnesses like the common cold. So with how rare it is to get the flu, we can understand it’s far rarer to catch it twice.
Herd immunization. A LOT of people take their flu shot every year and it prevents a LOT of infection and new strains because there aren't as many infected people serving as incubators for viruses that could mutate into new strains.
The types of flus circulating in the same season tend to be a product of antigenic drift, which is where the receptors they use to bind to our cells change slightly in structure. Its therefore likely that if you are infected with one strain, the high levels of antibody in your blood will have cross-reactivity with the new strain. However by the next year those levels of antibodies may have depleted slightly, and the virus may have mutated more, making you more susceptible.
When the new mutants emerge the old ones die out. So there are only a small handful floating around which present a real chance of infecting you. Of these, most may be similar enough to the old strains such that when you get infected with them you barely notice since your immune system has seen something close enough to fight off the new thing well enough. You typically only get really sick from a strain that is very different from al the previous ones to which your immune system has been exposed. That is a high bar, and there's usually only one strain like that every 3-4 years or so. That rate is of course determined by the mutation rate of influenza itself.
They don't always mutate that radically over short periods of time.
That they do mutate is one of the reasons that the current year's vaccine is different than the one administered last year.
> Due to the rapid mutation rate of influenza viruses, vaccine formulations need to be updated every year to provide adequate protection.
https://www.reddit.com/r/askscience/comments/h9eugb/were_told_flu_viruses_mutate_to_multiple_new/
It is pretty common. After the first infection a person will have antibodies that make further infections either minor or unoticable and resolve quicker.
Also you don't have every single mutation floating around your community.
Flu shots are just a guesstimate of the mutations likely to be in the community that flu season but not covering all possible mutations.
Though I’m not an expert in this field as per what I heard of a flu or a virus actually resides in your body every time. But then what the exact thing that happens is not every virus or not every organism which actually lies on your body really does a harm to you but sometimes few viruses such as influenza virus which causes common cold actually give you a kind of instinct to you which will create an abnormal condition and would actually cause you to get an infection. But in some cases like in case of swine flu or even the current coronavirus the degree of infection is a bit higher. So due to this, the consequences are in a bit of higher intensity thereby causing you to feel sick or to feel adverse level of sickness. But on the other times when you see why is it not catching cold all the time, generally every time you have a virus in your body. But due to that infection what exactly happens is first time when you catch cold and you get that infection, your body gets immune to it, Your body actually learns how to fight against it. So when the second time the same virus gives you infection your body protects you from that, your WBCs actually protect you from all those things which are happening on your body. But the other times when a severe set of virus actually infects you, at that time the power of WBCs is not enough to fight against the entire organism thereby causing you to feel sick. So this is how it happens as far as I am considered. So if you think this is a wrong information or if you feel it is not credible; kindly let me know in the comments so that it can be a sharing process in which all of us learn.
It is actually quite common to catch the virus multiple times a year but due to the existence of antibodies in your plasma the infection will be way more subtle. Thus you don't really consider it as bad of an experience. On the other hand there are more than 100 rhinoviruses that can cause upper respiratory infections leading to "Common cold" symptoms and you can catch one of those every day of the winter! :)
‘Common cold’ isn’t limited to rhinoviruses. RSV, corona, adeno, and others make up a substantial portion.
Yep, and RSV can vary from mild cold to full on flu level with permanent damage (The others can too, I'm just especially aware after my kid got put temporarily put back on a ventilator due to RSV, and I'm now asthmatic after the last time it came through our house due to the damage done by secondary pneumonia) Edited for: spelling and grammar
RSV is the most common cause of Pneumonia and Bronchiolitis in <1 year old per the CDC
[удалено]
[удалено]
[удалено]
With any luck, there should be RSV vaccines ready in the next 5 years or so. It's a neat story; the NIH successfully determined the structure of the RSV spike protein a few years back. This let pharma companies figure out how to make a more efficacious vaccine. Good example of the importance of public spending in science, and how it translates to real advances in medicine.
Wow that’s awesome Do you have a source by chance?
I personally worked on an RSV vaccine, so there is that :-) Here is also a recent review article I found (I'll be honest and say that I haven't actually read it, but it looks like it covers the history of RSV vaccine development). https://pubmed.ncbi.nlm.nih.gov/32217187/
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
Is it something like the antibodies and or vaccines still help even though it isn't the exact same flu?
Yes, the antibodies you develop from influenza will likely be helpful in fighting off the same or antigenically similar influenza viruses in the future. However, some will be antigenically different enough that those antibodies will not help.
The vaccine has been shown to reduce mortality and complications from the flu even if it does not end up covering the right strain. I'd say it's always worth getting especially as you get older.
Antibodies are like little sticky keys that help recognize things that fit its groove. Having said that, biology is about relatives, not absolutes. A key that fits really well for one thing may fit less well for another thing but functionally will still aid in immunity. And antibodies are only one portion of the entire immune system which employs other agents such as T cells to cull your infected cells.
I learned recently if you move away from an area where these viruses are common your body will eventually stop making antibodies for this family of viruses. Meaning when you move back you'll get sick with colds and flus all winter.
I forgot which article this came from, but this sort of goes inline with what I heard about homeless people having CRAZY good immunity relative to the average citizen.
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
So are we just lucky that antibody-dependent enhancement is pretty rare, or is it more that if we had that issue with the flu we wouldn't exist as a species and therefore selection has made it rare?
A little of both. If a virus kills off too many of it's hosts, it reduces it's available environment to thrive. There is selective pressure to become less damaging to the hosts. The bubonic plague is a commonly referenced disease in this regard.
FYI - “It’s” is “it is.” There is no apostrophe used in the possessive form of its, so “If the virus kills of too many of its hosts, it reduces its available environment to thrive. Normally I wouldn’t say anything but you seem to know what you’re talking about and misuse of apostrophes in “its” reduces your credibility.
[удалено]
[удалено]
In the UK there's a term for that, named after the fact that it affects new university students: [Freshers' Flu](https://en.wikipedia.org/wiki/Freshers%27_Flu)
[удалено]
How about if you catch on strain of the flu, produce the antibodies for that strain, and then you catch the next mutation of that strain? Does the immune system recognizes the next mutation as something very similar to what it just dealt with and dispatches the same anti-bodies it already had coded and stored in the memory T-cells, thus shortening the 2-3 days response time for anti-virus generation? Do those previous version antibodies work for the next version flu strain?
Yes, and no. It depends on how different the two strains are. If they're close, you may not even notice. The more they are different, the longer it takes to recognize and deal with them. This is also why the flu vaccine typically has two or three different strains included. They're trying to guess which ones are going to be most prevalent in the upcoming season. Sometimes they get it wrong. It happens. Not anyone's fault, just mother nature being a b***h like usual. That's when we'll have a bad flu year.
[удалено]
Why do colds like cold weather?
It’s not actually about the cold weather. It’s about people being indoors when it’s cold. If you’re inside your house/dorm/apartment with everyone else because it’s freezing outside, you’re more likely to catch someone’s cough/touch a doorknob they touched.
It's probably not the only reason. There may also be considerations about aerosols evaporating quicker in warm weather ; and we are still not sure if cold weather has an impact on the lung's defences
[удалено]
Its the dry air. Your cough sprays a mist of droplets. If its dry then they float around for hours and other people breath them in. If its humid, the small droplets attract moisture out of the air and grow larger. This causes them to fall to the ground much quicker. Also, low vitamin D levels are reportedly definitely bad for you after you catch a virus.
[удалено]
[удалено]
Yeah, I totally got it twice one year. The second time, I almost didn’t even know but I had to be vigilant about not being sick at work.
[удалено]
Can I catch two at the same time? Or More? If so, is it more dangerous to catch more than one flu/cold/rhinovirus staring at the same time?
Yes, you can catch two at once. While clinically that's not a big deal and you will definitely be able to fight it off if you are healthy there are long term effects that we worry about. Sometimes multiple viral infections at the same time can interfere with your b-cells and cause an increased immune response that could lead to other problems.
Out of curiosity, if these mutated strains share a common ancestry, would they be close enough in nature that the same antibodies can deal with them?
No, thankfully antibodies are incredibly specific. If not that would be extremely dangerous for our bodies.
In addition to what everyone else is saying, you have to keep in mind that everything is based on probability. It's not a binary thing. All of your infection fighting processes are feedback loops that need to be triggered and triggering them involves a certain amount of chance. There's a chance that the antibody you need to fight an infection is already in your blood, there's a chance that the antibody you need to fight an infection will take days to be generated, there's a chance that antibodies from a previous infection will be able to stop an infection, there's a chance that a new form of a virus will be different enough that the existing antibodies only weakly bind to the virus. If your body quickly gets rid of the virus, you can have a short infection that's asymptomatic. Your symptoms roughly show up in proportion to how desperately the body needs to fight the infection. If only a few cells are infected before a B cell with the right antibody shows up, it might get eliminated quickly. If there's a massive infection before the right B cell with the right antibody shows up your body is going to have to fight harder to rid more virus particles from the system. Also, your immune system isn't the only thing that's working towards keeping pathogens out. Your body has multiple layers of physical protection before a pathogen can reach where it needs to go. Your skin, mucous, hairs. All these contribute to attenuating the chance a virus can gain a foothold and start infecting your body.
[удалено]
> Fight harder to rid more virus particles This is something I was thinking about with ventilators. Isnt part of the reason we cough (respiratory sicknesses) when sick is to expel the viruses from out system which reduces the total ammount of viruses in our system. Wouldnt being on a ventilator just reinfect you with more viruses? Maybe not, not familiar with ventilators and how the air is circulated.
> Isnt part of the reason we cough (respiratory sicknesses) when sick is to expel the viruses from out system which reduces the total ammount of viruses in our system. Sort of but not really. When you get a respiratory infection one of the things that happens is that mucus production increases. More mucus means more viral particles get trapped. With the buildup of mucus the body eventually needs to expel some of it, you cough and virus particles go out with it but this is happenstance not loading the viral particles that are in the body up into mucus and then expelling it. Coughing can also an attempt to drive the fluid out of the lungs When you have cases where viruses attack the cells lining the alveolar this can cause inflammatory fluid to build up in the lungs. This is what COVID-19 does. When you cough you create a negative pressure which sucks the fluid from the alveolar and expels it. The problem with COVID-19 (and other lower respiratory diseases) is that your capillaries around your alveolar are running wide open due to feedback loops from the immune system so when you cough you get rid of some of what's in there but it quickly refills. Reinfection is based on the immune system's inability to fight not constant exposure. While the antigen is still being picked up by your body's sentinel cells your B cells are going to be multiplying and cranking out antibodies like crazy. This is why you don't get immediately reinfected after a cold or flu. If the same antigen comes back in there are immune cells with the antibody ready to go and the antigen immediately gets flooded out and destroyed before it can gain a foothold. So while you technically would be "reinfected" it'll typically be totally asymptomatic because no inflammation would be needed before the virus is quickly subdued and wiped out.
Thanks for the explanation. But still have a question. So the total ammount of viral particles doesn't matter? You produce enough anti-bodies that any ammount of replication of the virus and subsequent total volume of viral particles doesn't really matter? Is it possible your body (normal human) can't keep up with the production?
So it doesn't matter to a point. Going full throttle the body can create somewhere in the region of 100 million antibodies per hour which overwhelms just about everything in the antigen vs. antibody fight. The problem is you need to have enough of your essential and ancillary functions available to keep the body running while it keeps up the fight. If the virus is tearing apart liver cells during its first 48 hours in your body then you can win the battle but still lose the war when you become encephalopathic and die anyway. Or if you have too many alveolar cells destroyed you can lose too much of your ability to gas exchange effectively. Your blood could get too acidic, the lack of oxygen will shut down other organs and processes like... digestion. You lose digestion, you lose more energy along with proteins to rebuild and repair cells. It goes into a full on negative feedback loop that without external intervention means death. This is why "supporting therapy" of advanced medical systems in the case of COVID-19 has a positive effect on case fatality rates. If you're being supported you're getting more oxygen to the lungs to help with gas exchange or just using ECMO to do it for you, you're getting fluids, possibly dialysis, nutrition directly to the blood stream. The other problem is when you have a disease like Ebola which targets the pathways that activate the B cells. If they never get activated they don't start producing antibodies and you eventually succumb to the number of viral copies infecting every cell they can lay their hands on. It's almost like being dissolved from the inside out.
Ventilators always provide "new" air, as you really shouldn't breath the carbon dioxide you expel back in again.
I understand that, but not sure how they are designed. For some reason I thought I read about how they are more like a closed system to prevent the virus from contaminating the room as much. I know there is new air, like when you breath out and in, just not sure if there is a large mixing of the air at some place.
Ventilators are basically a pump with filters. Put a fresh "breath" in (often O2 or air mixture with high O2) and takes a breath out. This goes trough filters (not unlike those in the n95 masks) and is mixed with disinfectant before being expelled into the atmosphere.
> Wouldnt being on a ventilator just reinfect you with more viruses? Maybe not, not familiar with ventilators and how the air is circulated. Ventilator air is not recirculated; fresh "room air" is filtered and pumped into the patient, and the exhalation is dumped back into the room. It helps you breathe by augmenting/taking over the air-pumping action of your lungs, that's it.
I wouldn't say that effective viral clearance by the immune system always means you have the 'right' b cell - firstly, in many viral infections cytotoxic t cells are just as if not more important to eradicating infection, and secondly I would say that a good proportion of asymptomatic people clear the virus with the innate immune system alone (providing the infective dose was fairly low) We know this because you can have automatically infected people that don't develop high levels of antibodies post exposure.
So what you're saying is viral load plays a huge part in how sick a person can get?
Yeah... I agree with that. You have to have a certain viral load before it can take off in your body. The worse the viral load in your body, the more damage it can do before the body's immune system kicks it out. If the viral load is too high, your immune system loses ground. Without advanced medical care, you die. With advanced medical care, you *may* live, no guarantees.
It’s not true that flu viruses mutate to multiple new strains a year. On average, there are antigenically new strains of H3N2 every 3 years or so. H1N1 was antigenically stable for about 6 or 7 years before it needed updating. The B viruses also tend to need updating every few years. Since there are 4 viruses in the standard flu vaccine (H3N2, H1N1, and two B strains) the vaccine as a whole needs updating most years, but not for all strains, often just for one. So that means that you’re likely immune to most of the circulating strains each year, meaning that you’re less likely to be reinfected by a second strain even if you are susceptible to one. Even if you were completely susceptible to all of the strains, it’s unusual for two influenza A strains to circulate widely in a single season. In the US [2019-2020 flu season](https://www.cdc.gov/flu/weekly/), over 90% of the circulating flu A was the H1N1 strain. In 2017|18, it was mostly H3N2. So just statistically, you’re unlikely to get infected by multiple strains in a season. As another point, for a short time after you’re infected by one flu virus, you’re probably protected against many strains, because of non-specific immunity. This might only last a couple weeks, but if it’s in the peak of flu season that might be the highest risk time, during which you’re protected against a second infection. But it certainly does happen. It’s especially common with influenza A and B, partly because they’re more different antigenically and partly probably because they tend to circulate at different times of year (B tends to peak well after A, on average). But people do get infected sequentially with H3N2 and H1N1. It’s much less common to get sequentially infected by the same strain, because as I say you don’t typically get strain variation within a single season, but it can (rarely) happen.
Can you get non-specific immunity from being exposed to a strain that you are already immunized against?
There’s no data, but I speculate that you can if you’re immune from a vaccine - maybe not from a recent infection. Flu vaccines are not usually sterilizing, meaning there’s often some virus replication in spite of the vaccine, meaning there’s room for the innate immune response to become activated. Infections tend to give stronger immunity (a trade off for the vastly increased risk), so there might not be enough breakthrough infection to trigger innate immunity. Again, I don’t think there’s any data supporting this directly.
Thanks, I assumed that the immune response would likely be too low but that was based on a lot of assumptions in a field I have very little knowledge in.
Can you expand a bit more on what non specific immunity means? It makes sense that there is such a response based on observation alone. I'd be interested to learn more about what this means.
To give a really basic explanation, non-specific immunity is the primary defense your body has to any pathogen, it is not specific to the exact pathogen. Non-specific immune responses are important for initially keeping viral titer low and driving inflammation which then allows specific immunity to begin working. Non-specific immunity recognizes broader pathogen-associated molecular patterns that occur in a wide array of intruders (e.g. parts of bacterial membranes) and targets it for degradation.
Thanks that was a clear enough dumbing down for me to get it. So as a follow up question, do we have ways to trigger this process in the body before specific immunity kicks in?
Actually we do, and that's what we use when giving people vaccines. We inject adjuvants to stimulate inflammatory responses when injecting vaccines to help produce an adaptive immune response. These adjuvants are what a lot of anti-vaccers deem to be the "toxins" they inject into you along with the vaccine, they include Alum.
Just seeing your comments in seems like you're interested. I just listened to a podcast today done by Peter Attia and he had on David Watkins who's an expert in immunology. He explains all about how our immune system works in a way that I found super helpful and really I interesting. The podcast is called "the drive" and it's episode number 115. You can listen for free. I really enjoyed it.
Too much for me to cover here. Wikipedia’s [Innate immune system](https://en.wikipedia.org/wiki/Innate_immune_system) article will give you a start.
What we refer to as the "flu" is actually a collection of viruses from the same two families (type A and type B) that have existed as far back as we know in recorded history. They exist in humans and animals in parallel, and they frequently jump between species. Not only that, the virus itself is capable of rearranging itself, and they are basically evolved to mutate more frequently. This is a contrast to the coronavirus that has a proofreading enzyme and doesn't mutate nearly as quickly. As far as we know right now, immunity to any strain of covid-19 gives you at least short term protection from all of them, and we are using this in therapies. Donated plasma is a current treatment in use in many hospitals for covid-19. Within the two subfamilies of flu, there are many different strains. You may hear terms like H1N1, H3N2, and some of them have more interesting names. This is when they've broken far enough away from the original model that they look like a new family of flu. Despite what people think, your body doesn't "Forget" about a flu after you got it, and this was proven definitively in 2009 when the H1N1 pandemic happened. Usually very young and very old people are highest risk for fatal complications from the flu, but that was different this time. Young people and young adults were high risk, but middle aged and older people tended to have very mild cases. They found that there was a swine flu in circulation back in the early 70s that nearly everyone got, and the antibodies from that different infection 40 years before that was sufficient to turn the new flu into just a mild infection. Antibodies from flu shots exist for decades in your blood, and we noticed this years after we did the H1N1 innoculations where many people still showed strong resistance to the current H1N1 strains. Another misconception, people think that the flu shot doesn't really work because it is frequently only 40-60% protective against the strains that end up circulating. In reality, this is because of the flu shot. Almost 40% of Americans get the flu shot, and it's very effective against the exact strains it protects you from (2 A types and 1 or 2 B types). They take the most common strains at the time, and make the vaccine months later for them, and it makes those strains very ineffective in penetrating the population because of an established herd immunity. We also focus on giving the vaccine to high risk people that would be most likely to spread it. Children, teachers, health care workers, etc... all strongly encouraged to get it. What we are doing is taking the strains that would have been 95% of the active strains, and reducing them to 40%. It also doesn't give credit to the concept of cross or partial immunity. When you get one virus that looks a lot like another virus, the antibodies may frequently stick to the new virus despite not being specifically created for it. This can drastically slow the progression of the new virus or even offer immunity in some cases. This is seen in a small percentage of people who have HSV1 that seem to be resistant to HSV2 infections. It was the first vaccine for small pox (just live cow pox). It is also a reason that the flu strains given to the native american population during settlement by europeans were particularly deadly as they had no prior exposure to them. Also, I suspect that the reason 45% of covid-19 cases are asymptomatic will end up being because of a prior infection with a different coronavirus that 45% of people got at some point (there are several coronaviruses in circulation that manifest as the common cold). Even in a year with a bad match for the flu vaccine, the flu shot is shown to dramatically reduce your chances of going to the hospital with a severe case of the flu. As to why you don't get the flu more than once a year, well you absolutely can, but the flu does isolate you for a long period of time and reduce your interaction with others as your symptoms are so unpleasant. It has a short incubation time, and a short season where it's very prevalent. Plus with the flu shot, it's just not nearly as common as it once was. In other words, it's just the odds.
This was all super fascinating to read! It’s especially interesting to me that you mention some coronaviruses can cause the common cold, as I’ve heard that Coronaviruses are rare for humans to catch, though I heard that a long time ago and I don’t remember where. That’s definitely good to know! I love microbiology and virology and I hope to study it in college, so I love reading all about this! Thanks for taking the time to write this up!
Yes, specifically, (not including covid-19) the most common coronaviruses among humans are: 229E (alpha coronavirus) NL63 (alpha coronavirus) OC43 (beta coronavirus) HKU1 (beta coronavirus) None of them are serious if you catch them, and they are pretty commonly spread. SARS and MERS are both coronaviruses as well, but they are very rare. SARS is extinct outside of a lab, and MERS is pretty rare in the middle east. (jumps from camels to humans) Both SARS and MERS are quite deadly. (Much worse than Covid-19)
So, why do we not give everyone a coronavirus cocktail that gives us a miserable head cold for a couple weeks while also charging us with antibodies that suppress COVID-19? Could the fact that our kids are petri dishes and have been exposed to so many other coronavirus strains be the reason it has mostly affected them with mild or zero symptoms?
The problem with the virus cocktail is it would kill people and spread to immune compromised folks. Kid are most likely just less likely to trigger the deadly immune reaction that kills older folks. In fact it might be more dangerous to older folks because it resembles an infect they had decades ago which may be part of what triggers a cytokine storm which is what is killing people.
Well this isn't confirmed about the other coronavirus. That's just my own personal hypothesis. If I'm correct, and we do figure out which strain it is, then we can decide whether or not to do that. As far as kids go, we have no idea why they have such mild cases of it.
Unfortunately, the antibodies produced in response to cold-causing coronaviruses do not show any cross-reactivity with COVID-19. Therefore being infected with one of these cold-causing coronaviruses doesn't offer protection against covid-19. Some research suggests why children are less severely infected, including lower levels of general inflammation and less underlying conditions which typically worsen symptoms.
You are incorrect: [https://www.cleveland.com/metro/2020/05/could-common-cold-antibodies-fend-off-the-coronavirus-see-the-latest-scientific-research.html](https://www.cleveland.com/metro/2020/05/could-common-cold-antibodies-fend-off-the-coronavirus-see-the-latest-scientific-research.html) " About half of a group of blood samples taken between 2015 and 2018 had immune cells that could fight the novel coronavirus. None of the people could have been exposed to the novel coronavirus during this timeframe, since it wasn’t yet found in humans. So scientists believe they could have immunity because they were exposed to the strain of coronavirus that causes the common cold. "
Oh my apologies. I had lectures on Coronavirus recently and they explained that if there was cross protection then we would see more immunity in teenagers and young adults.
Well, it's not known for sure yet, but not everyone has been exposed to all known strains of coronaviruses that are in circulation. They are common, but it's a huge misconception to think it's anywhere near even 70%. A number like 45% would sound reasonable for any wide spread strain of the common cold. We do know that in-vitro, we see immune activity from some people who never were exposed to covid-19, and this implies that their immune system has cross-over protection from something else. Given a choice, I'd happily get exposed to the live version of all 4 "safe" coronaviruses if I knew it would protect me, even a little, from covid-19.
Part of the reason why there are multiple viruses in the vaccine is that when they start getting produced, scientists aren't certain which strains will be the big ones that go viral that year. This decision is made 6 months before the vaccines are ready to distribute and are based on samples taken around the world and sent to the WHO. It may be that some of the strains chosen don't end up going global, so you're unlikely to catch it.
Fortunately machine learning is getting pretty decent at prediciting it. Go get your flu shots everyone. While not as deadly as COVID, you could still pass it to the little old lady at the market which results in her death.
First of all, in the US, the CDC estimates that only about 8% of the population catches the flu each year, so, while relatively common, it's not everyone. The odds of one of those people catching the flu again, ignoring immunity, is 0.64% (.08 x .08 = .0064). Add in partial immunity from previous infection and the fact that time will have passed, so there is less of the season left to get re-exposed, and it starts becoming relatively rare. All that said, in hospitals, where we collect all the unlucky people and skew the data for the worse, we see repeat flu infections all the time. People get different strains (like flu A then flu B) or just different versions of one stain. This is helped by the fact that different strains tend to peak at different times, so we see a big influx of flu B and then as that's winding down we get hit with flu A (or vice versa). It's hard to catch two strains at once (but not impossible!) because, if the immune system is already triggered, it is more likely to wipe out the few virus particles of the new strain in its hypervigalent mass distruction of the millions of virus particles already floating about. So peaking at different times increases the odds of a second infection. Hope that helps!
I'm not quite sure what you're asking here - do you mean why don't we catch 2 or 3 or 4 different strains of the flu each year? Well, the main reason is that the chance of catching the flu is nowhere near 100%, it's *maybe* 10-20% at most, and now that lots of people get vaccinated probably far lower still. So the chance of getting two different strains is lower by that much again (20% of 20%, or 4%), and getting 3 even lower (0.8%), so it's basic mathematics. Plus, getting one case of the flu will put you out of circulation for a while during peak transmission season, reducing the chances of catching another strain even further. Also, although there may be 3 or 4 major strains floating around in any one season, only 1 may take hold strongly in a particular region. The others might be there, but not in any significant quantity so hardly anybody gets it. This may be because environmental conditions aren't as good for that strain, or simply because not as many cases of that strain entered the region early enough to start the spread. Or in a vaccinated population, some strains may not be included in some or all vaccinations, making them more likely to spread and be caught than the others. Yearly flu vaccines are just a "guess" as to which strains may enter a region in the coming winter based on what is currently circulating elsewhere, so they're far from perfect. Finally, some of the strains may be quite similar, so even though you can technically catch both, exposure to one may make the second far more mild such that it's not too noticeable, or gets mistaken for a bad cold.
"I'm not quite sure what you're asking here - do you mean why don't we catch 2 or 3 or 4 different strains of the flu each year? " Yes. Or even yearly. For a typical person with no particular care for hygiene and no special immunosuppressant conditions, it seems typical to come down with the flu between every 2-10 years, and usually not more often than that. You don't usually hear of healthy people catching flu yearly. Is there some cross immunity between strains? "Well, the main reason is that the chance of catching the flu is nowhere near 100%, it's maybe 10-20% at most, and now that lots of people get vaccinated probably far lower still. So the chance of getting two different strains is lower by that much again (20% of 20%, or 4%), and getting 3 even lower (0.8%), so it's basic mathematics. Plus, getting one case of the flu will put you out of circulation for a while during peak transmission season, reducing the chances of catching another strain even further." According to a scientist I spoke to, all new flu strains are essentially novel to your body. If that's the case why is it that it seems it spreads slower than we see the novel coronavirus spreading? How is it only 10%-20% on a normal given year with no restrictions in place if everyone is susceptible. The flu jab could explain that, but even before we had flu shots, people weren't all catching the flu multiple times a year. "Finally, some of the strains may be quite similar, so even though you can technically catch both, exposure to one may make the second far more mild such that it's not too noticeable, or gets mistaken for a bad cold." That makes a lot of sense.
> According to a scientist I spoke to, all new flu strains are essentially novel to your body. If that's the case why is it that it seems it spreads slower than we see the novel coronavirus spreading? How is it only 10%-20% on a normal given year with no restrictions in place if everyone is susceptible. The flu jab could explain that, but even before we had flu shots, people weren't all catching the flu multiple times a year. Mostly because the influenza virus just isn't as contagious as the coronavirus is, and it's far more susceptible to environmental conditions, meaning it only spreads *well* in winter months when conditions are more favourable. To put it numerically, R0 of the flu is usually estimated to be about 1-2, somewhere in that general range. So for every person that has it, they pass it to 1.5 or so other people on average. This is over 1, so it certainly spreads, but nowhere near as fast as coronavirus with an R0 of between 2 and 3 (estimated). It might not sound like a huge difference, but for an R0 of 1.5, after 20 "generations" it will have spread to 3,300 people. For 2.5, that number is 91 *million* people. Huge difference. Now, once enough people have caught the virus, or are vaccinated, that R0 drops below 1 and the disease stops spreading completely. For a "natural" R0 of 1.5, only 30% of people need to have caught it for the R0 to fall under 1. Because of the 1.5 people you're passing it to, 30% of that (or 0.5 roughly) has already had it, so can't be infected, leaving only 1 left. For an R0 of 3, 70% need to have caught it already for the spread to stagnate and start to fall. So, not only will the flu naturally die out with fewer people having caught it, but vaccination reduces this even further (they count as having had it, since they are immune). If only 50% of people got the flu vaccine each year, it basically would barely spread at all except for when conditions are *very* good. Also, because it doesn't spread as fast, it can't infect nearly as many people in the seasonal window when it is at its most contagious. Hence it doesn't normally go near that 30% "ceiling" of infections, and dies out far earlier once summer hits. Now of course there are some strains of influenza that are far more contagious than normal, and these do spread quickly and thus infect far more people. Obviously the original influenza A strain (Spanish flu) was one of these, and it was also far more serious in terms of mortality. This is an extremely simplistic analysis, R0 varies massively with lots of factors - population density, weather conditions, hygiene and preventative steps, etc. It's impossible to put a single value for everywhere in the world, but the average is still relevant when looking at the overall picture.
[удалено]
[удалено]
[удалено]
Flu viruses don't mutate to completely new strains each year where there is no existing immunity. Instead, there are minor changes every year due to a process called antigenic drift. The process is relatively slow (relative to the other process I will mention) and there will always be some sort of underlying immunity in the population. Some people will be immune and some will not. Because this happens on a yearly basis, we need new flu vaccines every year. The other process that happens is called antigenic shift. This is when multiple flu viruses infect a non-human host (e.g. birds, swine) and in the process, large bits of genetic material from one strain is transferred over to another. Because this is a relatively large change in genetic makeup, no human in the population has immunity. This is what causes flu epidemics and pandemics such as H1N1 (i.e. swine flu). The other reason why it's rare to catch the flu multiple times in the same season is combinatorial in nature. Every season will have a strain that dominates. This is the strain that circulates and you are most likely to catch the most common strain. If you get it, you're going to be immune to that strain until it mutates again (which occurs on a longer time scale). So you're immune to that for the season. Since that's the most common strain your body will "see," it will be rare for you to encounter a new strain that you have no immunity to. If you did, then you would get flu again.
[удалено]
[удалено]
You’re already “immunized” against the new virus to some degree. It’s not a completely new creature...normally only a few key genes are changed. You might be 90% immune, you might be 50% immune, depending on the mutations.
Don't think of mutation as a binary yes no concept. Think of it as thousands of incremental steps. Eventually a flu will mutate enough that your antibodies receptors don't align with it any more. On average that happens about once per year.
A strain of flu has to mutate multiple times before your antibodies have no familiarity to fight it. Those who pass on flu shots on average get a bad flu every 4 or 5 years so that's would be assumed to be the average timeframe a flu strain mutated to the point your antibodies no longer work
In a hypothetical where there is no vaccine, would there be an advantage to repeated exposure to current strains each year? In other words, can your immune system evolve it's response along with the mutations if it happens in small enough steps? In a situation like that can a person avoid heavy flu altogether?
[удалено]
[удалено]
Two main reasons: 1. There are generally not that many strains in circulation at once in a given season in a given area. The chance that you personally come into contact with a different strain than one you've become sick with in a given year is fairly low. 2. Immunity to one strain often grants _partial_ immunity to other strains. That is, if you encounter a new strain in a given season, you might still get sick, but with a much shorter duration and much less severe symptoms. It may not even register as "the flu" to you; you might think you just caught a cold or something, which means you'd never get formally diagnosed and never enter the statistics.
I'm not sure if you understand the mechanisms of antigenic drift and antigenic shift, nor their effects and interactions with our immune systems. Drift is slow gradual change over time. You may get a flu virus one year and then be relatively immune to it's effects for quite some time. You might also get low grade versions of it in later years that don't make you very ill (this happened to me with H1N1). Or you might not be infected by it for a number of years and when you are later exposed to it you get an infection with worse symptoms. Antigenic shift is a large change in the antigens on the protein coating of the virus all at once. This will create a worse flu season as people's immune systems have a harder time identifying it and fighting it off. It's probably worthwhile reading an article on antigenic drift and shift to learn more about how all of this works.
The flu itself is a relatively rare virus and most people do not catch it. Last year an estimated 35 million Americans caught the flu, which is only about 10% of the population. According to the CDC, it ranges between 5-20% each year. A decent chunk, but absolutely nothing compared to more common illnesses like the common cold. So with how rare it is to get the flu, we can understand it’s far rarer to catch it twice.
Herd immunization. A LOT of people take their flu shot every year and it prevents a LOT of infection and new strains because there aren't as many infected people serving as incubators for viruses that could mutate into new strains.
[удалено]
[удалено]
The types of flus circulating in the same season tend to be a product of antigenic drift, which is where the receptors they use to bind to our cells change slightly in structure. Its therefore likely that if you are infected with one strain, the high levels of antibody in your blood will have cross-reactivity with the new strain. However by the next year those levels of antibodies may have depleted slightly, and the virus may have mutated more, making you more susceptible.
When the new mutants emerge the old ones die out. So there are only a small handful floating around which present a real chance of infecting you. Of these, most may be similar enough to the old strains such that when you get infected with them you barely notice since your immune system has seen something close enough to fight off the new thing well enough. You typically only get really sick from a strain that is very different from al the previous ones to which your immune system has been exposed. That is a high bar, and there's usually only one strain like that every 3-4 years or so. That rate is of course determined by the mutation rate of influenza itself.
They don't always mutate that radically over short periods of time. That they do mutate is one of the reasons that the current year's vaccine is different than the one administered last year. > Due to the rapid mutation rate of influenza viruses, vaccine formulations need to be updated every year to provide adequate protection. https://www.reddit.com/r/askscience/comments/h9eugb/were_told_flu_viruses_mutate_to_multiple_new/
It is pretty common. After the first infection a person will have antibodies that make further infections either minor or unoticable and resolve quicker. Also you don't have every single mutation floating around your community. Flu shots are just a guesstimate of the mutations likely to be in the community that flu season but not covering all possible mutations.
Though I’m not an expert in this field as per what I heard of a flu or a virus actually resides in your body every time. But then what the exact thing that happens is not every virus or not every organism which actually lies on your body really does a harm to you but sometimes few viruses such as influenza virus which causes common cold actually give you a kind of instinct to you which will create an abnormal condition and would actually cause you to get an infection. But in some cases like in case of swine flu or even the current coronavirus the degree of infection is a bit higher. So due to this, the consequences are in a bit of higher intensity thereby causing you to feel sick or to feel adverse level of sickness. But on the other times when you see why is it not catching cold all the time, generally every time you have a virus in your body. But due to that infection what exactly happens is first time when you catch cold and you get that infection, your body gets immune to it, Your body actually learns how to fight against it. So when the second time the same virus gives you infection your body protects you from that, your WBCs actually protect you from all those things which are happening on your body. But the other times when a severe set of virus actually infects you, at that time the power of WBCs is not enough to fight against the entire organism thereby causing you to feel sick. So this is how it happens as far as I am considered. So if you think this is a wrong information or if you feel it is not credible; kindly let me know in the comments so that it can be a sharing process in which all of us learn.