Delta variant's spread seen pushing herd immunity threshold above 80%

Nearly 60% of Americans have received at least one dose of a coronavirus vaccine, and about 50% have been fully vaccinated

The spread of the delta coronavirus variant has pushed the threshold for herd immunity to well over 80% and potentially approaching 90%, according to an Infectious Diseases Society of America briefing on Tuesday.

That represents a “much higher” bar than previous estimates of 60% to 70%, because delta is twice as transmissible, said Richard Franco, an assistant professor at the University of Alabama at Birmingham.

“It is becoming clear that this is a very dangerous, way more dangerous virus than the original one,” Franco said.

Herd immunity is based on the idea that when a certain percentage of the population