The evidence — both from antibody testing and from epidemiological modeling — runs strongly counter to a theory being promoted in influential circles that the United States has either already achieved herd immunity or is close to doing so, and that the pandemic is all but over. That conclusion would imply that businesses, schools and restaurants could safely reopen, and that masks and other distancing measures could be abandoned.

“The idea that herd immunity will happen at 10 or 20 percent is just nonsense,” said Dr. Christopher J.L. Murray, director of the University of Washington’s Institute for Health Metrics and Evaluation, which produced the epidemic model frequently cited during White House news briefings as the epidemic hit hard in the spring…

Even in places where the pandemic hit especially hard — a French aircraft carrier, the Brazilian city of Manaus, the slums of Mumbai and a neighborhood in Queens, N.Y. — infections did not noticeably slow down until almost 60 percent of the inhabitants were infected. And even those levels may not suffice, given that cases are increasing again in Brazil and in Brooklyn areas that had seen cases spike and then drop off.

“Immunity in 2020 is no closer to being just around the corner than prosperity was in 1930,” said Dr. Thomas R. Frieden, a former director of the Centers for Disease Control and Prevention. “The route to immunity without a vaccine would be through graveyards filled with hundreds of thousands of Americans who did not have to die.”