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SACRAMENTO, Calif. — California updated its statewide mask guidance Wednesday, mirroring the Centers for Disease Control and Prevention in once again recommending face coverings indoors regardless of vaccination status.

The CDC’s update Tuesday recommended universal masking in areas where the coronavirus is making a resurgence. According to health officials, about 90% of California qualifies as an area of substantial or high transmission of the disease, and the new recommendation applies statewide.

“In California, unvaccinated persons continue to be required to wear masks in all indoor public settings. This guidance is an update, in light of review of the most recent CDC recommendations,” the state health department explained in an update to their online recommendations.

“To achieve universal masking in indoor public settings, we are recommending that fully vaccinated people also mask in indoor public settings across California. This adds an extra precautionary measure for all to reduce the transmission of COVID-19, especially in communities currently seeing the highest transmission rates. Local health jurisdictions may be more restrictive than this guidance.”

The state’s decision comes a day after San Diego County moved ahead of Sacramento and issued their own recommendation to follow the CDC’s new guidelines.

Most new infections in the U.S. continue to be among unvaccinated people. But “breakthrough” infections, which generally cause milder illness, can occur in vaccinated people. When earlier strains of the virus predominated, infected vaccinated people were found to have low levels of virus and were deemed unlikely to spread the virus much, CDC Director Dr. Rochelle Walensky said.

But with the delta variant, the level of virus in infected vaccinated people is “indistinguishable” from the level of virus in the noses and throats of unvaccinated people, Walensky said.

The data emerged over the last couple of days from 100 samples. It is unpublished, and the CDC has not released it. But “it is concerning enough that we feel like we have to act,” Walensky said.

Vaccinated people “have the potential to spread that virus to others,” she said.