“I think the most important thing to say is that California is starting the school year with all of our students masked,” Mr. Ghaly said.
Health officials will continue to monitor data and revisit whether to ease or maintain its mask mandate in schools no later than Nov. 1, he said.
The topic of school closures and reopenings has been particularly contentious since the onset of the pandemic, and advising districts has been a pervasive challenge for the C.D.C.
On Friday, the C.D.C. issued guidance urging schools to fully reopen in the fall and called on local districts to use local coronavirus data as guidance for public health measures.
The agency continues to recommend three feet of social distancing in classrooms, but in a departure from previous guidance, it says that schools can also combine other strategies, like indoor masking, testing and enhanced ventilation, if such spacing would prevent schools from fully reopening.
In another shift, masks are not mandatory for those who are fully vaccinated, according to the new guidelines. The C.D.C. continues to recommend masks for those who are not vaccinated, mirroring guidance for the general public.
In California and in New York City, average daily cases have increased in recent weeks, driven largely by the Delta variant, now the dominant strain in the country. But the overall number of cases remains low, and epidemiologists have said it was unlikely that the Delta variant would prove anywhere near as devastating as the past two waves of Covid-19.