https://www.scientificamerican.com/article/coronavirus-news-roundup-july-11-july-17/

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Dr. James Hamblin, a preventive medicine physician and a staff writer at The Atlantic, has written an essay that explores the concept of herd immunity, that is, the percentage of people needed to achieve immunity to prevent big spikes in a disease. For the current coronavirus, “some mathematicians believe that [the herd immunity level]’s much lower than initially imagined,” (that estimate was between 40 and 70 percent of the world’s population, per a Harvard University epidemiologist in February), Hamblin writes. The essay describes some models of SARS-CoV-2’s spread that make refined assumptions, such as a diminishing susceptibility of people who remain uninfected over time, and put herd immunity as low as 20 percent. But “the magic number that we’re describing as herd-immunity threshold very much depends on how individuals behave,” says an infectious diseases researcher at Georgetown University who is quoted in the piece. Hamblin concludes that “we have the wealth in this country [the U.S.] to care for people and set the herd-immunity threshold where we choose” (7/13/20).