(Bloomberg) -- U.S. health officials will return to tighter guidelines for the use of masks, advising that fully vaccinated individuals wear them in public indoor settings in places where the virus is spreading rapidly as part of a response to the spread of the delta variant.

The Centers for Disease Control and Prevention will recommend that teachers, staff, students and visitors to K-12 schools wear masks indoors regardless of vaccination status, according to a preview of guidance to be released later today. Children should return to full-time, in-person learning in the fall with prevention strategies in place, the preview said.

Anthony Fauci, the nation’s top infectious-disease expert, has warned that the U.S. is moving in the wrong direction in combating a new Covid wave spurred on by delta. CDC director Rochelle Walensky is planning a press briefing Tuesday afternoon where she’ll discuss breakthrough infections in vaccinated people and using masks to prevent further outbreaks in areas of substantial and high transmission.

A growing number of public-health experts have urged the agency to recommend that even fully vaccinated people wear face masks in public amid the resurgence of cases fed by the delta variant. Fauci said new U.S. recommendations on masking were under active consideration on CNN’s “State of the Union” Sunday.

Some places, such as Los Angeles County, have already revived mask mandates for public indoor places regardless of vaccine status. Former surgeon general Jerome Adams said the CDC acted prematurely in May when it announced that fully immunized Americans would no longer need to wear face coverings in most situations.

“The execution was poor, and the results speak for themselves,” Adams, said via email. “Low mask usage, slowed vaccination rates and exploding cases.”

The delta variant has prompted many countries to rethink their public-health strategies against Covid. However, as recently as July 22 Walensky said the agency was sticking with its recommendations that fully vaccinated people don’t usually need masks, while allowing that wearing one may have some advantages.

Covid fatalities in the U.S. surged 48% over the past week to a daily average of 239 and hospitalizations are also on the rise. The CDC says the delta variant now makes up 83% of all sequenced Covid-19 cases in the U.S., up from 50% at the beginning of the month. Areas of the country with limited vaccination coverage are allowing spread of the highly transmissible variant.

CNN reported the news earlier Tuesday.

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