Again: Viruses do not necessarily evolve to be milder—especially if they transmit early, like this one. Our immune system learning about it—via vaccines or infection—can mean better response next time, so milder experience. Not same as virus becoming intrinsically less virulent.https://twitter.com/zeynep/status/1465075561236250631 …
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Replying to @zeynep
This is a bold statement to make while we wait on omicron reinfection severity data. If a variant is sufficiently different, immunity from previous infection may not be effective. Consider how norovirus keeps causing the same gastro symptoms for all ages with each reinfection.
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Replying to @lisa_iannattone @zeynep
Just as there are many noroviruses and immunity from one doesn’t translate to immunity to another, immunity to one SARS2 virus may not translate to immunity to a sufficiently different SARS2 virus. We’re far too early in the course to be as certain about this as you seem to be.
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Replying to @lisa_iannattone
zeynep tufekci Retweeted zeynep tufekci
Not a bold statement. Everything else equal, of course re-infections are milder *on average*. We have so much data on this now. Two, as first tweet explains, a new variant is not everything else equal, so can be *more* severe to people with no immunity.https://twitter.com/zeynep/status/1465075561236250631 …
zeynep tufekci added,
zeynep tufekciVerified account @zeynepThis is a myth. Especially for a virus that can transmit early in disease course, like this one, selection pressure is on transmission, not virulence. So a new variant can be MORE or LESS virulent (when everything else equal, i.e. host immunity). https://twitter.com/soccervolleymom/status/1465074442044850183 …Show this thread3 replies 1 retweet 9 likes -
Replying to @zeynep
There’s actually not much data on severity of reinfections and much of the data we have doesn’t suggest a milder course for all. We could just as easily say primary infections are mild on average but the avg isn’t the story. The small % of a large number = many w severe disease.
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Replying to @lisa_iannattone @zeynep
Reinfection severity data that suggests many can have a more severe course the second time. And this was all pre-delta and pre-omicron. https://secure.jbs.elsevierhealth.com/action/getSharedSiteSession?redirect=https%3A%2F%2Fwww.clinicalmicrobiologyandinfection.com%2Farticle%2FS1198-743X%2821%2900422-5%2Ffulltext&rc=0& … https://www.cdc.gov/mmwr/volumes/70/wr/mm7008a3.htm?s_cid=mm7008a3_w … https://jim.bmj.com/content/69/6/1253 … https://www.medrxiv.org/content/10.1101/2021.10.04.21264540v1 …
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Replying to @lisa_iannattone
You can have cases here and there more severe—especially with strain changes. But I've seen all those studies. The key issue is the obvious, glaring conditional probability. You cannot only study the re-infections you encounter—obviously sicker than population-wide.
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Replying to @zeynep
You can make the exact same statement about primary infections. It was a popular anti-masker line early on that 99.5% of people survive. We can’t discount the small percentage that will go on to have severe disease on reinfection w VOCs that are increasingly more transmissible.
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Replying to @lisa_iannattone @zeynep
Small percentages of big numbers are big numbers. You know this.
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Not all discounting. The whole thread is about not assuming intrinsically less virulence. And yes, something can be milder, *on average*, and even by far, because of host immunity but still be a significant threat to sub-populations. In fact, I am writing a piece on this now.
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