This was a well plate containing patients’ samples being tested for SARS-CoV-2 antibodies, using the CDC serologic test. (James Gathany/CDC 2020)

Both Marin and Napa counties on Friday reported confirming their first case of the omicron variant of COVID-19.

Marin County officials said the person in their county had recently returned from a trip to the East Coast and was fully vaccinated but had not yet gotten a booster shot. That person is in isolation and has only mild symptoms. Napa County did not provide details about the positive case in their jurisdiction.

On Friday, those two counties and nine others in the greater Bay Area urged people to get vaccinated and to get a booster, if eligible, to protect against the rapidly spreading omicron variant.

Public officials in Alameda, Contra Costa, Marin, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano and Sonoma issued a joint statement encouraging people to get the shots either via appointment or at drop-in sites in their area.

People can get a booster shot if six months have passed since their second dose of the Pfizer vaccine if they are 16 and up, six months after their second dose of the Moderna dose for those 18 and up, and two months after their Johnson & Johnson dose for ages 18 and up.