The Centers for Disease Control and Prevention recommends that fully vaccinated people once again wear a face mask in public in areas with substantial or high transmission of COVID-19.

The Centers for Disease Control and Prevention (CDC) recommends that fully vaccinated people once again wear a face mask inside in public in areas with substantial or high transmission of COVID-19.

The latest CDC guidance is intended to protect people from the delta variant and prevent possibly spreading it to others, said CDC Director Rochelle Walensky, MD, MPH, in a media briefing late Tuesday.

“In recent days, I have seen new scientific data from recent outbreak investigations showing that the delta variant behaves uniquely differently from past strains of the virus that cause COVID-19,” she said. “Information on the delta variant from several states and other countries indicate that in rare occasions, some vaccinated people infected with the delta variant after vaccination may be contagious and spread the virus to others. This new science is worrisome and unfortunately warrants an update to our recommendations.”

Two-thirds of all U.S. counties have high (49.94%) or substantial (16.68%) community transmission, according to the CDC’s COVID-19 data tracker.

The CDC reports a 46.7% increase in the 7-day moving average of daily new cases since the prior week, 40,246 compared to 27,443. Latest estimates show the delta variant, first identified in India, is predicted to increase to 83.2% of all COVID-19 cases in the United States.

Walensky said vaccinated individuals represent a “very small amount” of COVID-19 transmission and that the risk of a breakthrough infection with symptoms upon exposure to the Delta variant is reduced by seven-fold. The vast majority of transmission, severe disease, hospitalization and death continues to be among unvaccinated people.

As of July 28, the CDC reported 57.1% (189.5 million) Americans have received at least one dose of the COVID-19 vaccine, and 49.5% (163.6 million) Americans are fully vaccinated.

In its updated guidance, the CDC says people may choose to wear a mask regardless of community spread if they or someone in their household is immunocompromised or at increased risk for severe disease from COVID-19, or if there are members of their household who are not fully vaccinated.

The CDC also changed its recommendation on COVID-19 testing among the vaccinated. Fully vaccinated people who have a known exposure to someone with suspected or confirmed COVID-19 should be tested 3-5 days after exposure and to wear a mask in public indoor settings for 14 days or until they receive a negative test result.

And ahead of a potential return to the classroom, the CDC recommended universal indoor masking for all teachers, staff, students and visitors to schools, regardless of their vaccination status.

“We continue to follow the science closely and update the guidance should the science shift again,” Walensky said. “We must take every step we can to stop the Delta variant and end this pandemic.”