The US Centers for Disease Control and Prevention recommended Tuesday that fully vaccinated Americans should return to wearing masks indoors if they live in an area with "substantial or high" transmission of COVID-19, highlighting the danger posed by the now-dominant delta variant.
Counties that have substantial COVID transmission have had 50 to 100 cases per 100,000 people in the past seven days, the agency said. Counties that have high transmission have had 100 or more cases of COVID in the past seven days. A CDC map of the US codes substantial communities orange and high communities red so you can find your county and its transmission rate.
CDC Director Rochelle Walensky made the announcement at a press briefing. She said there's new scientific evidence the delta variant "behaves differently" from variants of the past and that breakthrough infections in fully vaccinated people, though still rare, might be as likely to be contagious as infections in unvaccinated people.
"This new science is worrisome, and unfortunately warrants an update," Walensky said.
The CDC also announced a recommendation that all students, teachers and visitors at K-12 schools wear masks while indoors, regardless of vaccination status. In-person learning will still be a priority, as laid out by the CDC earlier this month. Children under 12 years old aren't yet able to get vaccinated against COVID. In addition to young children, the new recommendation may be directed at protecting immunocompromised people, who aren't as protected by the vaccines.
"On that exception that we might have a vaccine breakthrough, we wanted people to understand that they could pass this disease onto someone else," Walensky said.
At the briefing, Walensky said communities with low vaccination rates are experiencing a significant spread of COVID cases and are also seeing "severe outcomes." Even with the delta variant, the risk of COVID infection with symptoms is reduced sevenfold if you're vaccinated, while your risk of hospitalization or death is reduced twentyfold when vaccinated, she said.
Experts welcomed the new recommendation, with University of Washington professor of global health Ali Mokdad telling NBC that masks "work against every variant that this virus has produced" and Johns Hopkins epidemiologist Dr. Caitlin Rivers tweeting that "allowing vaxxed people to unmask may have had the side effect of everyone unmasking, vaxxed or not."
The recommendation also highlighted the CDC's tracking of breakthrough COVID infections, with some experts arguing that the CDC should track and release data for all breakthrough infections that occur in vaccinated people. As of May, the CDC documents vaccine breakthrough cases only if they result in hospitalization or death. When asked about the CDC's tracking of breakthrough infections at the briefing, Walensky said the CDC is collecting weekly data of milder infections on "cohorts" of people, tens of thousands of people nationwide, and that the CDC will report soon.