SAN RAFAEL (CBS SF) – Health officials in Marin and Sonoma counties reported their first cases of the COVID-19 omicron variant on Friday, as its rapid spread raises concerns in the North Bay and throughout the Bay Area.

Marin County public health officer Dr. Matt Willis confirmed Friday that a vaccinated resident who recently returned to the San Francisco Bay Area from a trip to the East Coast was the county’s first case.

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Willis added that the individual — who was in self isolation with mild symptoms — was fully vaccinated but had not yet received a booster shot.

“This confirms what we expected.” Willis said in a news release Friday morning. “Omicron is here, but we know what it takes. Getting a booster dose is the most important step. And stick with the steps that have protected us so far: get vaccinated, cover your face, ventilate rooms, and get tested often.”

In addition, health officials said, wastewater surveillance samples have detected low levels of Omicron in several collection sites across the county.

On Friday afternoon, officials in neighboring Sonoma County reported their first case of the variant.

According to health officer Dr. Sundari Mase, the variant was detected in a fully vaccinated person who had recently traveled within the continental United States. The person received their booster shot, but was less than two weeks out from their dose.

The Omicron variant has been detected in most Bay Area counties and is spreading rapidly globally and across the United States.

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On Thursday, Dr. Sara Cody, Santa Clara County’s public health director, said there were now 10 cases of the variant, one week after confirming the county’s first case. The variant has also been found in all four wastewater treatment plants in the county, while it was found only in one treatment plant a week ago.

Health officials cautioned residents that a surge in local cases across the region is very likely in the coming weeks. Infections with the new variant are seemingly less severe and are not yet driving surges in hospitalizations and deaths in the areas where its most prevalent globally.

“Much remains to be learned about how Omicron behaves,” said Dr. Lisa Santora, Deputy Health Officer for Marin County Public Health, said in news release. “Its unwelcome news at this stage in the pandemic, but we have a lot of control over our risk. We’ve benefitted from high vaccination rates so far, and we’ll continue to lean into the protection of vaccines to meet the next challenge.”

Officials said evidence was mounting that initial doses aren’t enough to effectively prevent against infection with the Omicron variant. Health officers in all Bay Area counties renewed calls Friday for people to receive their booster doses.

“Even if you were fully vaccinated earlier this year, two shots are no longer enough. We know protection from the vaccines declines over time, so booster doses are critical for everyone 16 and older who was vaccinated at least 6 months ago,” Mase said.

In Marin County, 87% of eligible Marin residents have been fully vaccinated. About 95,000 residents, almost half of those eligible, have received a booster dose.

Meanwhile in Sonoma County, where 75% of eligible residents are fully vaccinated, only 30% have received their booster shot.

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