Shouldn't these viruses get selectively better at fighting human immune systems? And we're throwing 750.000 new hosts to this virus worldwide every day.
I'm sure there are other factors, but that's a big one. So most viruses tend to harm the host less over time.
We saw the opposite effect during the Spanish Flu. As I recall at least one theory: because there was a war on, only severely sick soldiers would get sent away from the front lines, where they could come into contact with the general population. Less severe cases were kept on the front lines. This behavior created an inverse effect, applying selective pressure on more _severe_ strains of the virus. Hence, the second more deadly wave.
Once the Spanish Flu pandemic was "over" and the war was over, that pressure wore off and the Spanish Flu slowly evolved into various common cold strains that we still see today (AFAIK).
My guess is that it's hard to speculate what will happen with COVID-19. Several common cold viruses are coronaviruses, so from that one might conclude that COVID-19 will follow the same path of becoming less severe over time. But COVID-19 also has a _very_ large incidence of asymptomatic transmission. So isolating people who are very sick is unlikely to provide much selective pressure to this virus.
If COVID-19 _does_ become less severe over time, it will occur only because of different selective pressures or for different reasons. For example, maybe the mutations that result in higher transmission also, by some genetic necessity, lower severity.
The asymptomatic nature of COVID-19 gives it a big question mark, and we should _not_ assume anything about it becoming less severe over time. We should keep up aggressive measures to control its spread and lean on our vaccines to squash it before it has a chance to get worse. The quicker we get the vaccine out, and the more aggressive we are about controlling the virus's spread, the higher our chance of getting out of this mess.
Does it? Meta-analysis concluding secondary attack rate in households from asymptomatic transmission around 0.7%.
> Household secondary attack rates were increased from symptomatic index cases (18.0%; 95% CI, 14.2%-22.1%) than from asymptomatic index cases (0.7%; 95% CI, 0%-4.9%)
https://jamanetwork.com/journals/jamanetworkopen/fullarticle...
Make a convincing study to disprove them.
Actually if you read the meta-analysis I linked, 0.7% secondary attack rate covers both presymptomatic and asymptomatic.
> The asymptomatic nature of COVID-19 gives it a big question mark
Also the mass, un-targeted lockdowns have probably screwed with the selective pressure as well.
So, there are two suggestions within viral genetics:
1. Mutations which are kinder to the immune system might be able to spread relatively easier. As noted in the other comments, this is likely dependent on human behaviour and ritual around illness and death.
2. Significant mutations which spread more efficiently are perhaps more likely to knock-out genes causing harm (lost to 'evolutionary cost') than to enhance those genes.
Neither of these are completely guaranteed, but they are generally seen as likely.
the virus will not become weaker as time goes on, it will have less variation to call upon for evasion of host defenses.
the major selective pressure on this virus appears to be exhaustion of variant production bringing the cat and mouse game of new viral antigen sequence vs antibody respecification to a stalemate, and the virus must move on [spillover] to a new host species. The ability to occur in many novel variations, and eventually spillover from a host species to a conspecific host is how this virus persists.
> Trade-offs between different components of parasite fitness provide the dominant conceptual framework for understanding the adaptive evolution of virulence (Alizon et al. 2009).
...
> By far, the most widely studied trade-off involves transmission and virulence (Anderson and May, 1982; Frank, 1996; Alizon et al. 2009).
But. I have no training.
I remember the scientists telling us early on in the pandemic that mutations typically result in less lethal viruses.
Is this not the case?
If any (will), it shouldn’t be killing its host.
These are anthropomorphic reasoning and antagonisms.
What would you say instead, to capture these ideas, that are equally clear to everyone?
In general, a "weaker" virus has an evolutionary advantage. Killing or disabling the host means fewer opportunities to spread.