But the basic idea is that the pandemic itself seals its own doom by depleting population susceptibility, just as a forest fire ensures its own end by burning up all the fuel. And it overshoots: so by the time the pandemic is over, the R(effective) is LESS than 1.
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So: game over for the virus, right? Erm, no. That decline in R is transient. Susceptibility in the population starts to reaccumulate, both because of waning immunity in infected/vaccinated individuals, and because of accumulation of newly minted baby-people in the pop
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who replace the elder-people at the other end of the life span as they die. That results in repletion of susceptibility. The virus (as with flu, as maybe with sars2) can also lend a helping hand by mutating over time (we call this "drift") with flu, and becoming...
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...sufficiently different from previously circulating strains that it de facto increases population susceptibility. We see this play out every year or two with very drifty flu. It's one of the reasons we have to keep changing the flu vaccine (which has 2 different A antigens)
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But that's not a pandemic, for two reasons: 1. We have a much lower R because of prior population immune experience. 2. Those who have been around longest (older people) have prior immune experience.
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And are protected against these resurgences by earlier exposure. That's why the 2009 pandemic was mild. Those who would be most likely to die from a novel resp infection had prior lifetime immune experience. Not the case in 2019-2021.
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So be confident. The idea of a forever-pandemic is about as plausible as the idea of a forever-forest fire. Not gonna happen.
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Viruses replicate a lot faster than we do, so they always have a head start on anything that depends on mutation. It is likely that we'll challenges over time as novel variants, maybe even vaccine escape mutants, emerge.
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And I would expect that even with immunization we will continue to see seasonal and off-season outbreaks of covid-19 in crowded institutional settings (and cruise ships) which have been hotspots for outbreaks long before there was a COVID-19 pandemic.https://pubmed.ncbi.nlm.nih.gov/16276954/
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I hope that's helpful. There's more to say here, but it's coffee time. COI declaration: I study infectious diseases for my job, and I think it's dumb for people to die of communicable diseases unnecessarily.
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zeynep tufekci Retweeted David Fisman
Thank you! I spent a good chunk of last February trying to explain the "novel" part to friend telling me about the flu. (I mean, yeah get your flu shot...) Now, it's a bit reversed, the lowered susceptibility (infection+vax) is almost disregarded.https://twitter.com/DFisman/status/1357665128884424705 …
zeynep tufekci added,
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