Ajay Sethi, a public health professor with the University of Wisconsin-Madison, said in the absence of a vaccine, the disease’s spread slows only in one of two ways: because the population achieves “herd immunity,” where most people are protected from prior infections, or because people follow public health practices. And every available study, Sethi said, shows Americans are nowhere close to herd immunity, and that attempting to achieve it would require mass infections and deaths.
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