“Manaus was the first city to have its health system collapse in the new wave,” says Brazilian physician and neuroscientist Miguel Nicolelis. The threshold for COVID herd immunity is unknown, but projections often cited range from 60 to 90 percent. The response from public officials, they say, was always the same: herd immunity would protect them. Wearing masks and practicing social distancing had been discarded in the belief the city had reached herd immunity. Questions arose as to whether herd immunity had ever been achieved, the number of people infected had been overcounted or immunity to the virus had waned.