3 ms·

Can you elaborate on why a lockdown would select for a more virulent strain?

Izkata 6y ago
I'm mainly basing it on the graphs provided: The cases don't spike until after the "G" strain is present, no matter how long the "L" and "S" strains were present beforehand. Actually I think I should have said "infective" rather than "virulent" there; basically lockdowns select for versions of the virus that can spread despite the lockdowns. It only looks more virulent because of the larger number of total infections.
- chimprich 6y ago
  It's worth bearing in mind that the graphs in the article are quite distorted. Testing was not widely available until months into the pandemic, making the early spikes look much smaller than they were. Later strains may indeed turn out to be more infectious, but I don't think we have the evidence for that yet.
- divbzero 6y ago
  Based on the graphs alone it’s also possible that more infective strains lead to spikes which lead to lockdowns.
  - LeCow 6y ago
    To which it will become more contagious more quickly...
- usrusr 6y ago
  As long as the epidemic doesn't run close to saturation (and given the multiple effective vaccines it likely won't, ever), NPI-induced relative spread advantages of one strain over another don't make a difference unless they are also absolute advantages compared to non-NPI-scenario. And given the strength of pre- and asymptomatic spread of this particular virus, it's almost immune to selective pressure for weaker symptoms anyways (scarcity of PCR and deep connect tracing can cause some pressure).
gcanyon 6y ago
Not an evolutionary biologist, but I think it's better to think of it as potentially killing off an earlier, less virulent strain. Putting it in concrete terms, if you have two versions of the virus, X which for each infected person tends to infect 1.8 others, and Y which tends to infect 2.8 others, then after ten days there might be more people infected with Y than X, but X would still be around. Now if everyone takes precautions, maybe those rates are cut in half. Now X only infects 0.9 people per infected person, and thus dies out, while Y is still infecting 1.4 people per infected person, and thus is still spreading, just slower.
- craftinator 6y ago
  > Putting it in concrete terms, if you have two versions of the virus, X which for each infected person tends to infect 1.8 others, and Y which tends to infect 2.8 others, then after ten days there might be more people infected with Y than X, but X would still be around. This is actually an observed effect in many transmittable illnesses; over time, they become more transmittable, and less deadly. Extremely deadly forms kill their hosts, ending the ability to reproduce via transmission, and the more transmittable strains reproduce effectively. This type of optimization leads to things like the common cold and flu. The scary thing about COVID19 is that it has a very long lead time between infection and symptoms, if they develop at all, meaning it can circumvent some of those "normal" optimization peaks; it can be both very deadly, and very transmittable, because of the latency in the signal.
hedora 6y ago
Imagine the original strain had a mortality rate of zero, but later strains had high mortality rates. The original strain would effectively be a vaccine. The lockdown would be the equivalent of the anti-vaxxers. There’s no evidence the mortality rate has actually increased; this was just a thought experiment. In prior pandemics (1918 flu), future strains were more deadly than earlier strains. The nightmare scenario now is that a COVID-20 emerges with a 5% mortality rate instead of 0.5%. If catching COVID-19 gives you immunity to COVID-20 (and all the vaccines fail), then the lockdown would increase the death toll by 10x. These are all hypotheticals that looked somewhat plausible in April, and implausible today.
deleted 6y ago
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rolph 6y ago
[N.B. mods, deleted accidental dupe comment] a lockdown would select for a more communicable strain, not a more virulent strain. the big problem is this virus has morbidity latent to infection incubation and transmission. these conditions mean that the virus can be 100% lethal and not succuum to the usual dynamics

I'm mainly basing it on the graphs provided: The cases don't spike until after the "G" strain is present, no matter how long the "L" and "S" strains were present beforehand. Actually I think I should have said "infective" rather than "virulent" there; basically lockdowns select for versions of the virus that can spread despite the lockdowns. It only looks more virulent because of the larger number of total infections.

chimprich 6y ago
It's worth bearing in mind that the graphs in the article are quite distorted. Testing was not widely available until months into the pandemic, making the early spikes look much smaller than they were. Later strains may indeed turn out to be more infectious, but I don't think we have the evidence for that yet.
divbzero 6y ago
Based on the graphs alone it’s also possible that more infective strains lead to spikes which lead to lockdowns.
- LeCow 6y ago
  To which it will become more contagious more quickly...
usrusr 6y ago
As long as the epidemic doesn't run close to saturation (and given the multiple effective vaccines it likely won't, ever), NPI-induced relative spread advantages of one strain over another don't make a difference unless they are also absolute advantages compared to non-NPI-scenario. And given the strength of pre- and asymptomatic spread of this particular virus, it's almost immune to selective pressure for weaker symptoms anyways (scarcity of PCR and deep connect tracing can cause some pressure).

gcanyon 6y ago

Not an evolutionary biologist, but I think it's better to think of it as potentially killing off an earlier, less virulent strain. Putting it in concrete terms, if you have two versions of the virus, X which for each infected person tends to infect 1.8 others, and Y which tends to infect 2.8 others, then after ten days there might be more people infected with Y than X, but X would still be around. Now if everyone takes precautions, maybe those rates are cut in half. Now X only infects 0.9 people per infected person, and thus dies out, while Y is still infecting 1.4 people per infected person, and thus is still spreading, just slower.

craftinator 6y ago
> Putting it in concrete terms, if you have two versions of the virus, X which for each infected person tends to infect 1.8 others, and Y which tends to infect 2.8 others, then after ten days there might be more people infected with Y than X, but X would still be around. This is actually an observed effect in many transmittable illnesses; over time, they become more transmittable, and less deadly. Extremely deadly forms kill their hosts, ending the ability to reproduce via transmission, and the more transmittable strains reproduce effectively. This type of optimization leads to things like the common cold and flu. The scary thing about COVID19 is that it has a very long lead time between infection and symptoms, if they develop at all, meaning it can circumvent some of those "normal" optimization peaks; it can be both very deadly, and very transmittable, because of the latency in the signal.

hedora 6y ago

Imagine the original strain had a mortality rate of zero, but later strains had high mortality rates. The original strain would effectively be a vaccine. The lockdown would be the equivalent of the anti-vaxxers. There’s no evidence the mortality rate has actually increased; this was just a thought experiment. In prior pandemics (1918 flu), future strains were more deadly than earlier strains. The nightmare scenario now is that a COVID-20 emerges with a 5% mortality rate instead of 0.5%. If catching COVID-19 gives you immunity to COVID-20 (and all the vaccines fail), then the lockdown would increase the death toll by 10x. These are all hypotheticals that looked somewhat plausible in April, and implausible today.

deleted 6y ago

[deleted]

rolph 6y ago

[N.B. mods, deleted accidental dupe comment] a lockdown would select for a more communicable strain, not a more virulent strain. the big problem is this virus has morbidity latent to infection incubation and transmission. these conditions mean that the virus can be 100% lethal and not succuum to the usual dynamics