Delta Pushes Herd Immunity Threshold To Above 80%: Experts

"It is becoming clear that this is a very dangerous, way more dangerous virus than the original one," an assistant professor at the University of Alabama at Birmingham said.

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 has been vaccinated against the virus or gains immunity by a previous infection, it helps protect the broader population and reduce transmission.