Hopefully title covers the question. All of the above are viruses and I understand that the latter two mutate. Wouldn’t the first ones I listed also mutate over time? Is the difference more a function of type of vaccines, or the viruses themselves? Why does this difference in preventative care exist? I think even the new RSV vaccine is a single does. Looking forward to understanding this better. TIA
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You got it right, some viruses simply mutate more rapidly and have different variants, while others don’t. It depends on their preferred replication mechanism, which allows for different rates of mutation.
Coronavirus for example mutates incredibly fast, so we need to keep the vaccines updates, while Shingles is really stable, so one vaccine is enough.
That said, there’s another factor at play here, which is immune memory. Some viruses and bacteria elicit a greater immine response, and the protection lasts for a long time, sometimes for a lifetime.
Other microorganism instead generate a weaker immune response, and after some time the immune system needs to “see” the virus/bacteria again to relearn how to deal with it.
At its very simplest, viral vaccines work by teaching your body to recognize viruses from a distance, basically how to recognize their shape and outline. Your immune system is basically just on the prowl comparing the outline and shape of every thing it sees to a list it keeps in it’s pocket, like an old timey Police Officer looking for outlaws.
Chicken Pox, measles, polio, etc., those viruses haven’t really changed much since they first started infecting people. Nothing magic or special, it’s just that those viruses don’t spend their Level Up XP on changing their shape. So once they are added to your immune system’s list, they can be spotted pretty much forever. It is worth nothing though that those lists are essentially get photocopied over time and after 20 or 30 years can be pretty rough looking so it might be smart to make the list from scratch again – to get a new vaccination.
The ‘corona viruses’ though, the family of viruses that include SARS 1, SARS 2 (COVID), and the Flu absolutely *do* spend their level up XP on changing their shape. In fact that’s the only thing they spend their XP on. Just change shape change shape change shape with every single level. You might have noticed we keep talking about new COVID strains and subtypes and mutations? Corona viruses are like hermit crabs, constantly changing their shells. So pretty much impossible to learn to fight only by looking at their silhouette and shadow.
What we do with the Flu, which is very seasonal, is see what it “looks like” in the Northern Hemisphere, get like 6 or 10 of those general shapes and make them into a cocktail to give to the Southern Hemisphere in their winter 6 Months later. Then we see what’s up in the Southern Hemisphere and repeat it with the northern 6 Months later. This is why we sometimes miss and end up with bad flu years when it changes into something we didn’t see coming.
It’ll probably be like that with COVID, with use using a cocktail of “we think it looks like this” sketches and shifting it up 2x per year as new strains emerge.
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A disease evades vaccination by changing into different variations of itself. Diseases mutate based on two factors: how many people have the disease and how unstable is the disease?
COVID spreads around a lot more than chicken pox. That gives it more opportunities to change into a variant.
COVID is also much less stable than many other diseases, meaning it can change a lot faster.
That combination means COVID regularly changes enough to evade vaccines.
However, it’s important to know that even an old, out-of-date vaccine gives you better protection than being unvaccinated. The new vaccine is an attempt to update your defenses against the newest variants.
Measles, Varicella (chicken pox/shingles) and polio are human specific diseases, they don’t infect other species (which is why it would be possible for them to be eradicated if antivaxxers didn’t exist).
All viruses mutate to some extent but Influenza mutates rapidly. It has a segmented genome, meaning instead of having one big piece of DNA or RNA, it has 8 pieces. If two different strains of flu infect someone at the same time they can swap entire pieces of genome allowing a totally new strain to form essentially overnight. Even worse, flu infects a lot of different animals, so a human flu virus can infect pigs or birds, etc and swap RNA with animal flu viruses and then return to humans in a totally different form. This is likely how 1918, 1957, 1968, 1977 and 2009 pandemic flu strains formed. Coronaviruses act in a similar way, infecting different species and then jumping to humans and rapidly mutating as they go.
So each year new flu strains circulate and new vaccines are needed. Coronaviruses mutate rapidly and so boosters are needed, although they are different from flu in that new coronavirus strains now are progressive variants of SARS-CoV-2 rather than the stepwise differences we see in influenza (thanks to its segmented genome and seasonality).
New coronavirus outbreaks tend to happen every decade now: OC43 likely caused the 1889 pandemic, HKU1 crossed to humans in ~1995, SARS caused the [2002 pandemic](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3329048/) (halted by the WHO), MERS caused a [2012 epidemic](https://www.who.int/health-topics/middle-east-respiratory-syndrome-coronavirus-mers#tab=tab_1), SARS-CoV-2 (COVID) caused the 2019 pandemic, in all likelihood we will see more coronaviruses jump to humans and will need new vaccines for them. (Most people had never heard of coronaviruses until now but this is at least the 3rd major outbreak caused by a coronavirus)
The exception to this is HIV, which is a human specific virus but it mutates rapidly due to the nature of [how it replicates](https://en.m.wikipedia.org/wiki/Retrovirus). Which has made HIV vaccination incredibly difficult (among other things).
So there are a lot of factors. How much it mutates isn’t the only thing. It’s also limited by how much it even can mutate. There are only so many different working combinations for each virus. And some of those combinations aren’t different enough, so your bodies recognition will treat them the same anyway.
Your body also keeps antibodies for more dangerous viruses around longer. You could get sick with the same flu virus that you had a few months after you’ve already had it. Because it takes resources to keep those antibodies at an elevated level.
You can think of it like mall security. If shoplifting gets really bad they’ll bring in more people for a bit to stop it, and then when it calms down they’ll let the staff go.
Shoplifters can take stuff 100 different ways, so while security is trained in catching the “stuffed jacket” shoplifter, they’ll miss the “Hides inside other boxes” shoplifter. It’d be way too costly to train in every single way so you only train in the way people are doing it right now.
But a guy walking in with a mini gun, there’s not really a way he can change up his method. He can paint it hot pink but people are still going to know what it is. Security will stop anyone that walks in with a minigun once they’ve seen it once. And you’re always going to have some security around trained in stopping that because of the harm it could do.
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