04-03-2020, 11:29 PM
(This post was last modified: 04-03-2020, 11:29 PM by panamaniac.)
(04-03-2020, 11:17 PM)danbrotherston Wrote:(04-03-2020, 07:57 PM)MidTowner Wrote: Doesn't it remain in circulation until some critical proportion of the population achieves immunity, either through having contracted it or having been administered a vaccine? And the more we slow the spread, the longer the former takes. And since a vaccine is twelve or eighteen months or more away, two years seems reasonable, or even ambitious.
The answer to the first part of your question is, no, it doesn't have to remain in circulation.
SARS (v1?) died out, because everyone who was sick with it got better or died, and there were no new patients, thus the virus died out (of the human population anyway). The key to doing this is controlling the R0. This is much harder for a virus like SARS-CoV-2 because it's R0 is much higher to begin with (for various reasons including pre- and a-symptomatic transmission), but it is still possible to get R0 under 0 and thus starve the virus of new hosts. China has already (or at least claimed to have) done this in specific areas.
If you can do this in a local area then you can shrink the infected population then reduce restrictions while controlling new cases through tracing, testing, travel restrictions, and quarantining, you can be free of a virus, even without herd immunity. In theory at least--I think we're yet to see if this is possible in practice with this virus but the short answer is no, it's not necessarily the case that everyone must get the virus before herd immunity is acquired.
It's also not necessarily the case that "everyone getting it" would actually provide protection either, this virus does mutate, and while I think experts haven't seen it mutate sufficiently to avoid new immunity (nor do experts even know how long or effective acquired immunity is for this virus), it's entirely possible that it could mutate in that way in the future, just as the flu and cold viruses do every year. In fact, again, I'm not an expert, but I believe that everyone getting it, would make it more likely that it would mutate in that way.
I am curious though, why you believe that a vaccine that is available in 18 months would take 2 years to give us herd immunity? I believe the 12-18 month estimate is for broad availability of the vaccine--and we're already 2 months into that timeline.
Don't most vaccines take about two weeks to generate immunity? I guess longer if it's something that requires a booster.