Not a doctor, this is not a rhetorical question: Shouldn't we have those 2nd-time sick people by now? Shouldn't the null hypothesis be that immunity works like most other colds?
Masks weren't "proven to be effective" until well after any reasonably thoughtful person was wishing they had one.
- of 4 coronavirus strains in one study (all the type that cause common colds), none gave long term immunity after exposure
- of those 4 strains, getting re-infected multiple times in the same year is common
- each person tends to have a consistent reaction (weak/strong symptoms the first time through predict a similar experience in any later infections)
- infection severity tends to run in families
- 6 years after SARS, doctors found T-cells, but no B-cells in humans . Mice re-infected with SARS were protected from the worst effects or SARS by memory T-cells.
Specifically related to covid-19:
- macaque monkeys were infected by covid-19 and exposed again 4 weeks after recovery. none developed symptoms or had detectable virus in their throats
- no reported cases of re-infection in Wuhan in the 5 months since the epidemic started
Maybe if there was no infection induced resistance, but with even moderate resistance lasting a few weeks, probably not outside of Wuhan, and it's not like we can be confident we'd get accurate information on that.
> Shouldn't the null hypothesis be that immunity works like most other colds?
Colds are mostly rhinoviruses, this is a coronavirus, so, no, you wouldn't by default generalize from colds. Coronaviruses don't particularly consistently produce long-term reliable immunity, instead what immunity they do produce typically wanes quickly. So the best assumption would be that whatever resistance getting infected confers is likely quite limited in duration.
