Across the country, the latest COVID-19 surge is being driven by the highly transmissible BA.5 sub-variant, prompting concerns that it could mean a return of broad indoor mask mandates in cities.

The school district’s decision to reinstate indoor masking came after San Diego County moved into the “high” category of community transmission set by the U.S. Centers for Disease Control and Prevention (CDC) guidelines.

Indoor masking will be required at all schools and district offices for at least two weeks, the district said in a letter on Friday.

“We will continue to monitor the COVID-19 community level according to the CDC and County data and we will communicate if there are any changes in two weeks,” the letter said.

“If your student is participating in summer school or other summer enrichment program, please send them to school or their program with a mask. If they do not have one, masks will be provided. Students and staff will be required to wear their masks while indoors only.”

San Diego Unified’s board president, Dr. Sharon Whitehurst-Payne, defended the policy in an interview and said students who don’t want to wear a mask should not return to summer school.

Asked what students who are not comfortable wearing a mask should do, Whitehurst-Payne told KUSI-TV: “They really should wear the mask.”

Pressed on the issue, she said: “They should just let… make it known that they don’t feel comfortable and at that point, just not return.”

Whitehurst-Payne added that if the indoor mask mandate is still in place when the fall semester begins, students have the option of learning remotely if they don’t want to wear a mask.

“They can go to our school that’s online,” she said. “They can opt not to return to the regular school but to go to the school where they don’t have to go to school at all other than via Zoom.”

Whitehurst-Payne has been contacted for further comment.

Some colleges in California have also reinstated indoor mask mandates. The University of California Irvine said masks would be mandatory inside campus building for all individuals, regardless of vaccination status, from Monday.

UCLA reinstated an indoor mask mandate in late May and later said the policy would remain in place until further notice.

Los Angeles County—California’s most populous county and home to 10 million people—will reinstate an indoor mask mandate on July 29 if community transmission remains high, county health Director Barbara Ferrer said during a media briefing on Thursday.

“With the high rates of transmission fueling the increased risks, sensible safety precautions that can slow down the spread of the virus are warranted,” Ferrer said.

While she acknowledged that it will “feel like a step backwards” for many, she added: “We are not closing anything down. We are not asking people not to gather with the people they love… We’re asking you to take a sensible step, when there’s this much transmission with a highly transmissible variant, to go ahead and put back on a well fitting high-filtration mask when you’re indoors around others. And I think that’s the prudent thing to do.”