Napa, Santa Cruz and Monterey counties were the latest addition to areas that recommend its locals to mask up indoors amid the increase of COVID-19 cases.

On Monday, the three counties released a combined advisory, along with San Benito County, to advise its locals to wear masks when they are in indoor public spaces like retail and grocery establishments, theaters, and entertainment facilities.

The four counties’ health personnel recognized the worrying increase in cases, especially among the unvaccinated population, but cleared that the plan does not include the re-implementation of the full mask requirement.

“Fully vaccinated people are well-protected from infections and serious illness due to COVID- 19 including the Delta variants,” the counties said in their combined statement. “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.”

“Out of an abundance of caution,” the same guidance was earlier issued by Contra Costa, Alameda, Santa Clara, San Francisco, San Mateo, Sonoma and Marin, as well as the city of Berkeley.

Public health officials from the local, state and federal government cautioned the spread of the pandemic. Unvaccinated people have more risks of contracting the virus, and even death, as compared to those who have completed their vaccines.

After the state opened on June 15, unvaccinated residents were mandated to use face-covering in indoor areas while fully vaccinated people were not required to. However, the social control in carrying out the mandate for unvaccinated individuals has been reliant on self-authentication, SFGate reported.

Local businesses in the four counties are being encouraged by health officials to boost their anti-virus efforts by following the universal mask requirements when welcoming their customers inside their premises.