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the highest credible estimate of COVID's base R value in the United States (i.e. pre-March 1) is 3, which suggests you only need 66% immunity to keep R durably below 1 with virtually no measures in place.
people asking about how UK/SA variants play into this.
The studies of those variants assume that the ZERO MITIGATION R value for "old COVID" is about 2.6.
They say the ZERO MITIGATION R value for "new COVID" is about 3.9.
Post-mitigation, it's 0.85 and 1.25.
The studies of those variants assume that the ZERO MITIGATION R value for "old COVID" is about 2.6.
They say the ZERO MITIGATION R value for "new COVID" is about 3.9.
Post-mitigation, it's 0.85 and 1.25.
To estimate the herd immunity threshold, you use the zero-mitigation value (i.e. Base R or R0). So those studies suggest we need 62% immunity for "normal COVID" and 72% for "new COVID."
Once we correct for some ballpark estimates of what resistance vaccines/prior infections provide to old/new strains, we can estimate we have the equivalent of about 26% current immunity to old COVID and about 6% current immunity to new COVID.
However, as I showed in yesterday's death day, we're vaccinating now much faster than "all COVID" is spreading, and it's likely that vaccine efficacy will rise (new boosters, continuing research, more options, etc).
Right now the US R value is about 0.9. If we were all "new COVID," it would probably be a lot higher, like 1.4 (where it was in December), even with current mitigation measures.
But the key point is that the true share of people who need to get vaccinated is *not* 85% or something. Even with current vaccines, we only need about 37% more of the population vaccinated before we've basically beaten "old COVID."
Beating "new COVID" is harder due to the higher R, lower background resistance, and lower vaccine efficacy. To beat it, at least one of those has to rise, and we better hope it's NOT "background resistance" (i.e. number of people previously infected).
Pushing R down is hard; it's not clear that current measures or anything like current measures will really achieve that kind of reduction.
So this is an argument for getting as many vaccines in arms as possible pronto.
So this is an argument for getting as many vaccines in arms as possible pronto.
And expediting approval of boosters.
With pessimistic assumptions:
1) Old COVID infection gives truly zero protection against new COVID
2) Vaccines are just 60% effective against new COVID
3) New COVID has infected few people so far
4) New COVID has R(0) of 3.9
Herd immunity is impossible. We hit 100% exposure.
1) Old COVID infection gives truly zero protection against new COVID
2) Vaccines are just 60% effective against new COVID
3) New COVID has infected few people so far
4) New COVID has R(0) of 3.9
Herd immunity is impossible. We hit 100% exposure.
In this scenario, U.S. excess deaths run up to like 4 million.
So it's extremely important that we beat old COVID while we can and expedite permitting for boosters ASAP.
