Delta variant drives herd immunity' threshold over 80%

The Infectious Diseases Society of America said that the alarming spread of the delta coronavirus variant has pushed the threshold for herd immunity to well over 80% and potentially almost 90%.

Earlier, it required an estimated 67% of the population to be vaccinated to achieve herd immunity.

According to its media briefing on 3 August, it could be time to consider wearing an N95 mask in public indoor spaces, regardless of vaccination status.

"The problem here is that the Delta variant is … more transmissible than the original virus. That pushes the overall population herd immunity threshold much higher," Ricardo Franco, MD, assistant professor of medicine at the University of Alabama at Birmingham, said during the briefing.

"For Delta, those threshold estimates go well over 80% and may be approaching 90%," he said.

Herd immunity is the point at which enough people are immunized that the entire population gains protection. And it's already happening. "Unvaccinated people are actually benefiting from greater herd immunity protection in high vaccination counties compared to low vaccination ones," he said.

Measles has one of the highest herd immunity thresholds at 95%, Franco added.

Indonesia is effectively ditching its bid for herd immunity as delta pushes the threshold beyond reach. 

Thailand had record deaths and cases, while Australia found an infection in the far-north city of Cairns. Macau is shutting bars and cinemas, and there's growing concern about the outbreak in mainland China.

US President Joe Biden criticized the pandemic response of the Florida and Texas governors, both Republicans. The two states account for about a third of all new US cases in the past week.