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by nfc
2236 days ago
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So from what you are saying the explanation for the paragraph from the article would be that a more severe infection would be more likely to have R0 < 1, so on aggregate viruses would "commonly" evolve this way. I understand this, but thank you for the reminder of the mechanism :) However if the the R_0 of COVID-19 is between 1.4 and 5 (https://en.wikipedia.org/wiki/Basic_reproduction_number), how likely would it be that another mutation more lethal would appear and still be successful?, that is with R_0 > 1. I think that's a more relevant question than whether most successful mutations will be less lethal. Specially knowing that one of the characteristics of the virus is asymptomatic spread which could invalidate the point of a more lethal strain having much lower R_0. |
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R0 is not necessarily inherent to the virus (although I think australia might use a more restrictive definition that makes it more inherint to the virus), it's based on our behavior to a large extent. MinuteEarth has a great video (i'll link it below) that discusses how Cholera, for example, stayed very severe and yet had a high R0 because it spread through sewage and the sanitation system was not so great, so it didn't matter whether people stayed home since their fecal matter ended up in drinking water anyway. But after sanitation systems improved, cholera's R0 dropped and the less severe mutation meaning higher r0 thing kicked in since you needed more human interaction to get it to spread again.
So with coronavirus, if it mutates to become more severe, maybe it'll mutate back to a SARS like form where it's super lethal which also means it doesn't spread really far. Both SARS and ebola are on that end of the spectrum. But let's say people get overconfident and think they've beat it and don't stay home in the earlier days of the infection when they're not bedridden yet, you could still get a lot of spread. Or, let's say it becomes more severe, but also gains the ability to survive on surfaces for weeks and become airborne when dislodged. Now, your santation procedure for your instacart delivery is no longer enough and the virus could keep spreading through a lockdown. And then there are diseases like HIV, which are ultimately incredibly severe, but have a latency period that allows for infection to keep occuring even with a mechanism of transmission that is a lot more effortful than accidentally coughing near someone. As you mentioned, the asymptomatic spread aspect has echos of htis, where even though the mutation could be severe, it might not have the chilling effect on transmission you'd expect because of asymptomatic and presymptomatic spreaders.
So long story short, I don't know how likely it is that a more lethal mutation appears, but I do think you're right in intuiting that it is possible. Perhaps there are ways to estimate a probability by running simulations on the genome of the most common types of mutations to see what sort of effects we can anticipate. SARS-COV-2 is very closely related to SARS-COV after all, it's just a slightly different straing, even though the SARS outbreak and the COVID outbreaks look so different. I don't think it's impossible that COVID could mutate to have SARS' severity while maintaining COVID's presymptomatic shedding and asymptomatic spread. Maybe as we learn more about it we'll discover that both come from the same mutation and it's a fundamental tradeoff, but I think it's possible that that's not the case.
A disease's guide to world domination from minuteearth: https://www.youtube.com/watch?v=Ch4d9qEKmHE