Health officials in seven Bay Area counties — Alameda, Contra Costa, Marin, San Francisco, San Mateo, Santa Clara and Sonoma — on Friday urged vaccinated people wear masks again indoors to prevent the spread of the highly infectious delta variant of the coronavirus. The officials said in a joint statement that while fully vaccinated people are well protected from developing serious illness from all coronavirus variants, asking everyone to wear masks indoors can help protect unvaccinated people. A universal rule makes it easier to verify that unvaccinated people are masking up, the officials said.