The COVID-19 pandemic

[danbrotherston]

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.

I understand that getting the ratio down to close to 0 is possible, but the possibility of doing that here in Ontario seems remote. Further, even if we could, we will remain open to other jurisdictions to some extent (I would say a large extent, depending on the perspective you take). There is no chance that we will close our borders completely. The deprivation wouldn't be worth it by anyone's estimation, I don't think. While there are cases somewhere, there is a chance that they will spread here. And that's even if

My understanding was that 12-18 months was an extremely ambitious timeline, possible but never before achieved, so this is why I think projecting the presence of the virus for two years seems logical. But I was under the impression that the timeline was ambitious for having the vaccine acceptable, not broadly available. If 18 months is the timeline for a vaccine to be validated and administered broadly, then I guess that's the timeline for the virus to be eradicated.

(By the way, both 18 months and two years are very long lengths of time to have anything like the kinds of controls and shutdown we're experiencing now...)

We don't have to get it close to 0, we have to get it under 1...I misspoke.

For getting it under 1, that's entirely possible, somewhere, I'm not sure where, estimated that with China's restrictions, which are obviously impossible here, it got down to 0.3, which results in a strong negative growth rate (I'm not sure I understand the math right, but I believe it would shrink at a rate close to the growth rate with an R0 of 3, which means it will shrink faster than it grew).

We don't have to get that low, but anything under 1 would result in negative growth. And yes, travel will be restricted for a long time, it will be very bad for tourist destinations. But with tracing and testing, it appears possible to keep this virus under control without strong local restrictions. This is exactly what many Asian countries are doing right now. Yes, they have differen contexts from ours, but if we can shut down half our economy for 6 months, I believe we can also implement similar controls. The even bigger benefit is that we have a model to follow for achieving that.

As for vaccines, an 18 month timeline would be extremely ambitious for a new vaccine, but again, much of the work has already been done, meaning a 12-18 month timeline is instead reasonable. If one of the first vaccines they are testing is successful, then 12 months is very much in play.

Edit: Some data: https://medium.com/@Joe_C_London/covid-1...9e485b0c63

While the author of this is not a healthcare expert, nor a contageous diseases expert (and can be a bit....overconfident sometimes) he generally backs up his opinions with numbers. If a peak has been reached in those countries, then the R is less than 1, so it's entirely possible. I think the restrictions are more severe in those countries, but it still demonstrates it is possible in western democracies.