Everyone should wear masks in public indoor settings in regions with high COVID-19 transmission rates, the Centers for Disease Control and Prevention recommended July 27.

The new guidance is a reversal from CDC’s May 13 guidance that vaccinated people did not need to wear masks in most settings. The change comes on the heels of new science on the delta variant of SARS-CoV-2, the virus that causes COVID-19.

“Information on the delta variant from several states and other countries indicates that in rare occasions, some vaccinated people infected with the delta variant after vaccination may be contagious and spread the virus to others,” CDC Director Rochelle Walensky, MD, told reporters in a media briefing.

With schools opening in fall, CDC also called for universal masking for all teachers, staff, students and visitors in schools, regardless of their vaccination status. As of July 18, only 35% of children ages 12-17 have received at least one vaccine dose. 

“For many Americans, this advice is a dramatic reversal of where we were just months ago, when we seemed to be turning a corner against COVID-19,” said APHA Executive Director Georges Benjamin, MD, in a statement. “But science has shown increasing rates of infections, leaving CDC with no choice but to change its recommendation, which we applaud." 

Fully vaccinated people may also choose to wear a mask regardless of transmission level if they or their household members are immunocompromised or are susceptible to severe disease from COVID-19. 

CDC continues to strongly recommend that everyone who is eligible become vaccinated. According to tracking by The Washington Post, about 49% of eligible people are fully inoculated against COVID-19, and nearly 57% have received at least one dose. Almost all people hospitalized for COVID-19 or who have died from the disease in recent weeks have been unvaccinated.

State and local policies requiring mask-wearing “will likely need to be reinstated,” said Barbara Alexander, MD, MHS, FIDSA, president of the Infectious Diseases Society of America, in a statement. 

“It is imperative that state and local health officials are empowered to determine the mitigation measures necessary in their communities to end this pandemic,” Alexander said.

Walensky urged community leaders to support vaccination and universal masking. 

“The highest spread of cases and severe outcomes are happening in places with low vaccination rates and among unvaccinated people,” Walensky said. “This moment — and most important, the associated illness, suffering and death — could have been avoided with higher vaccination coverage in the country.” 

People can learn about their county’s COVID-19 transmission level through CDC’s COVID Data Tracker and find a COVID-19 vaccination site at vaccines.gov.