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The study’s goal was to estimate the impacts of a single “super-spreader” event on the spread of COVID-19.

USA TODAY

By the end of July, about 9% of American adults had been exposed to the coronavirus that causes COVID-19, according to a new study of dialysis patients, the largest yet looking for evidence of the disease in people’s blood.

The infection rates varied from essentially zero in some states that avoided infection by midsummer, to more than one-third of residents in parts of New York hard-hit in the spring.

The upshot is the American public is a long way from achieving “herd immunity” – having enough infections to prevent further spread of the virus. 

Infection rates are so patchy that even if some areas have had high infection rates, people there are unlikely to be protected because others will bring the virus in from elsewhere, said William Hanage, an