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San Francisco Bay Area health officials on Friday urged residents to again wear masks inside public buildings, offices or businesses regardless of whether they are vaccinated.

The counties of San Francisco, Santa Clara, San Mateo, Marin, Alameda, Contra Costa, Sonoma and the city of Berkeley stopped short of requiring masks indoors. But officials in those localities said wearing them will ensure all unvaccinated people are masked in those settings.

The region stopped requiring those who have been vaccinated to wear a mask indoors last month when California fully reopened its economy and did away with social distancing and capacity limits for indoor businesses and restaurants.

The Bay Area has seen some of the highest vaccination rates in the state. Several of the area’s seven counties have at least 80% of their residents 12 and older vaccinated with at least one dose.

The announcements came Friday amid a spike in COVID-19 cases, most of them the highly transmissible delta variant that has proliferated since California fully reopened its economy on June 15. The vast majority of new cases are among unvaccinated people.

“Vaccinating as many people as possible, as soon as possible, continues to be our best defense against severe COVID-19 infection, and the harm it can do to our region,” officials said in a joint statement.

On Thursday, Los Angeles County officials announced residents will again be required to wear masks indoors, regardless of their vaccination status. Also, the University of California system said that students, faculty and staff must be inoculated against the coronavirus to return to campuses.

The rapid and sustained increase in cases in Los Angeles County requires restoring an indoor mask mandate, said Dr. Muntu Davis, public health officer for the county’s 10 million people. The public health order will take effect just before midnight Saturday.