The Centers for Disease Control and Prevention (CDC) said today fully vaccinated individuals should wear masks in certain indoor areas and advised universal masking for schools regardless of individuals’ vaccination status amid rising infections due to the delta variant.

“In areas with substantial and high transmission, CDC recommends that fully vaccinated individuals wear a mask in public indoor settings to help prevent spread of Delta and protect others,” the agency wrote ahead of a briefing. Though rare, breakthrough infections do occur in fully vaccinated individuals, however, unvaccinated populations account for nearly all current hospitalizations and recent deaths.

In a significant shift from prior guidance, the health agency also recommended “universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status.”

“In recent days, I have seen new scientific data from sequenced outbreak investigations showing that the delta variant behaves uniquely differently from past strains of the virus that cause COVID-19,” CDC Director Dr. Rochelle Walensky told reporters over a call. “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,” Walensky said.

Walensky sidestepped whether the new guidance would remove incentive for some parents to seek vaccines for kids.

The CDC previously advised masks be worn indoors by all individuals ages 2 and older not fully vaccinated against coronavirus. The CDC previously stated that those who are fully vaccinated didn’t need to wear a mask or physically distance in any setting, including while participating in extracurricular activities or while eating. However, it noted that based on the needs of the community, a school may opt to make mask use universally required regardless of vaccination status.

The CDC urged those not yet vaccinated, and eligible to receive a COVID-19 vaccine, to do so, writing: “Unvaccinated individuals should get vaccinated and continue masking until they are fully vaccinated. With the Delta variant, this is more urgent than ever. The highest spread of cases and severe outcomes is happening in places with low vaccination rates and among unvaccinated people.”