COVID Milestone

On March 22, 2020 there were about 8500 cases of COVID reported in the US. The number has never been that low since. Today there were less than 7500 cases. While numbers typically dip on Sundays it’s still quite a milestone. Hopefully the true beginning of the end. (But with variants and vaccine reluctance who knows).

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Oh wait…here’s the real milestone. Costco: Free samples, foood courts will return fully by June

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I am extremely encouraged. Early on, estimates of R0 of COVID-19 were a little all over the place, but consensus seems to have emerged that it’s between 1.5 and 2.5. Meaning theoretical herd immunity attaches when between 33% and 60% of the susceptible population is immune, whether thorough antibodies following prior infection, vaccination, natural immunity/ nonsusceptibility or some combination of those.

With 50%+ of the adult population (including 75% of the elderly) and 40%+ of the entire population of the United States fully vaccinated, we are just about there. Very encouraging.

This meta-analysis suggests an R0 of around 2.87, but cautions that different studies’ results were highly variable: Reproductive number of coronavirus: A systematic review and meta-analysis based on global level evidence . The “more contagious” B.1.1.7 variant probably has a higher R0 than what was circulating before that meta-analysis.

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At R0 of 2.87, theoretic herd immunity attaches at 65%. No need to go crazy and hold out for 80%+ vaccination rates.

However, R0 among non-immune people is probably higher now since the B.1.1.7 variant has become dominant in the US and many other places.

Herd immunity is probably not much of a concern for most vaccinated people, but it is a large concern for those who cannot get vaccinated for medical reasons, and those who do not get a good immune response from vaccines.

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