| IANAV: So, when someone gets visibly sick, they tend to get isolated from other people. That makes it more difficult for the virus to spread. So over time there's a slight advantage to variations of a virus that don't make as many people sick. 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...