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Comment by voidmain | Hacker News Reader

Even if the whole world was in sync, you more or less have to hold Re below 1 forever or accept that 1-1/Re of everyone gets the virus. That's basically a tautology. But Re can be affected a lot by testing and tracing when the infected population is tiny compared to your resources, and not so much when it is huge. Re could also be affected a lot if we had a vaccine, which will probably take years in the current regulatory regime but is something that might actually benefit from disparate international approaches.

It wouldn't be crazy to ask international travelers to pay the marginal cost of extra testing and/or the negative externality of spreading the virus between worse and better controlled regions.

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1) buy time by reducing Re

2) invest into medical research

3) hope you can manufacture something effective by the time the next wave hits

Don't think y our 1-1/R0 rate makes sense (I assume Re is equivalent to R0 - I'm not familiar with Re). At an R0 of 1, each person spreads to one other person. So everyone would eventually be infected, just at a linear rate. Your formula though gives 1-1/1 = 0. Similarly for an R0 less than 1 your formula goes negative.

Anyway, if R0 can be brought below 1, it wouldn't need to be indefinite. The further below 1 it is, the faster the virus will extinguish itself. This was seen in China, where they went from exponential growth to fewer new cases each day and ultimately to the situation now where most new cases are imported from other countries.

You also don't need global coordination, although it helps. Any individual country can restrict outside travel from outbreak areas, get their own R0 below 1 via social distancing to eliminate the local outbreak, and then relax social distancing locally, relying on travel restrictions and temporary quarantines of travelers from outbreak areas, plus testing and contact tracing. If cases start to flare up again, increased social distancing measures can be brought in to get them back under control.

So in theory you could do extreme distancing for a period on the order of a few months, and then normalize somewhat. It would take a global response of that sort (unlikely), a vaccine, or a change in the virus itself though to end the situation entirely.

At an R0 of 2, with no interventions, eventually half the population has had the virus and (hopefully) gained immunity. Now each person only spreads it to 1 other person, because the other person they would have infected is immune. (If R0 was 1, the epidemic would end as soon as the next person in the chain is immune.) This is where the people saying that the virus will definitely eventually infect 70% of everyone are coming from.

Re is effective spread rate, taking into account natural immunity, vaccination, contact tracing, etc. By definition, if Re>1 the epidemic is growing exponentially and if less it is shrinking.

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