Los Angeles County will again require masks be worn indoors in the nation’s largest county, even by those vaccinated against the coronavirus, while the University of California system also said Thursday that students, faculty and staff must be inoculated against the disease to return to campuses.

The announcements come amid a sharp increase in virus cases, many of them the highly transmissible delta variant that has proliferated since California fully reopened its economy on June 15 and did away with capacity limits and social distancing. The vast majority of new cases are among unvaccinated people.

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 go into effect just before midnight Saturday.

“This is an all-hands-on-deck moment,” Davis said during a virtual news conference.

He didn’t fully detail what would be some exceptions to the mask rule but said, for example, people could still take off their masks while eating and drinking at restaurants.

Davis said officials will focus on education rather than enforcement. Handing out citations to people who don’t comply is “not something we really want to have to do,” he said.

Los Angeles County has been recording more than 1,000 new cases each day for a week, and there is now “substantial community transmission,” Davis said. On Thursday, there were 1,537 new cases, and hospitalizations have now topped 400.

“The next level is high transmission, and that’s not a place where we want to be,” he said.

It comes after a winter where Los Angeles County experienced a massive surge in infections and deaths, with hospitals overloaded with COVID-19 patients and ambulances idling outside, waiting for beds to open.

Now, hospitalizations in California are above 1,700, the highest level since April. More than 3,600 cases were reported Thursday, the most since late February, but a far cry from the winter peak that saw an average of more than 40,000 per day.