(WASHINGTON) — The Centers for Disease Control and Prevention on Tuesday reversed its mask guidance to specifically target areas of the country with the highest levels of the coronavirus and recommended that everyone in those areas, vaccinated or not, wear a mask as the delta variant continues to spread rapidly across the U.S.

The public health agency also recommended schools embrace universal masks, departing from guidance released earlier this month that suggested vaccinated students and staff were safe to go without.

“CDC recommends localities encourage universal indoor masking for all teachers, staff, students, and visitors to schools, regardless of vaccination status,” the CDC wrote in a summary of the new guidance. “Children should return to full-time in-person learning in the fall with proper prevention strategies are in place.”

CDC Director Rochelle Walensky cited new scientific data from a recent outbreak investigation, as well as data from other countries, to defend the agency’s decision to urge vaccinated people to return to wearing a mask in some parts of the country.

She said the data show the delta variant “behaves uniquely” from past strains of the virus.

The data indicate that on “rare occasions, some vaccinated people with the delta variant … may be contagious and spread the virus to others. This new science is worrisome and unfortunately warrants an update to our recommendations,” she said.

Last May, the CDC took the country by surprise when it announced guidance that all vaccinated Americans were safe to go without a mask indoors or in a crowd. Its guidance for schools followed that principle.

The CDC recommendations noted that individuals and schools could still opt to wear a mask even if fully vaccinated, but said the risk of illness and transmission was low.

On Tuesday, two months after the initial guidance was released, the agency told reporters that the risk of severe illness from COVID still remains low for Americans who are fully vaccinated and the vast majority of people hospitalized with COVID-19 are still unvaccinated.

But the delta variant, which has taken root in the U.S. over the last month and now represents 83% of all infections, is different than past mutations of the virus, the CDC said.

“In rare occasions, some vaccinated people can get delta in a breakthrough infection and may be contagious,” the CDC said.

Ahead of the CDC’s announcement, ABC News White House correspondent Karen Travers asked press secretary Jen Psaki what the White House’s message is to Americans who may now rethink even getting a vaccine with these conflicting recommendations.

“We continue to be at war with a virus, an evolving pandemic,” Psaki said in response. “Our responsibility here is to always lead with the science, and always lead with the advice of health and medical experts and we’re going to continue to provide information to all of you about how to protect yourself and save your lives. We’re not saying that wearing a mask is convenient, or people feel like it, but we are telling you that that is the way to protect yourself protect your loved ones and that’s why the CDC is issuing this guidance.”

ABC News’ Justin Gomez contributed to this report.

This is a developing story. Please check back for updates.

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