More than 91 million live in US counties with high Covid-19 infections. It's time to reset and put masks back on, expert says

With the highly contagious Delta variant spreading, particularly among unvaccinated Americans, it may be time to hit the "reset button" on pandemic response and for much of the country to put masks back on, an expert said.

"We are at a very different point in the pandemic than we were a month ago," Dr. Leana Wen told CNN on Tuesday. "And therefore, we should follow the example of LA County and say that if there are places where vaccinated and unvaccinated people are mixing, then indoor mask mandates should still apply."

Los Angeles County reinstated a mask mandate over the weekend, requiring masking indoors regardless of vaccination status.

Wen, a CNN medical analyst, said there are two exceptions to the occasions she thinks people should be wearing masks indoors in public: when everyone is vaccinated and has provided proof or if there is a very high level of community vaccination.

Ideally, mask mandates would be in place while leaders move toward methods of proving vaccination status to boost vaccination rates, said Wen, an emergency physician and visiting professor of health policy and management at the George Washington University Milken Institute School of Public Health.

But about 28% of the US population, or more than 91 million people, lives in a county considered to have "high" Covid-19 transmission, according to data from the US Centers for Disease Control and Prevention. Only 48.7% of the total US population is fully vaccinated against the virus, according to the CDC -- a number far below the 70% to 85% health experts have estimated it would take to slow or stop the spread.