Ninad Dhuri takes off his mask to eat with fellow San Jose State University students Rinkle Anuwadia (left) and Divya Mutha (right), at Dr. Martin Luther King, Jr. Library in San Jose, Calif., on Oct. 6, 2021. (Harika Maddala/ Bay City News)

Marin, San Francisco, Sonoma and Alameda counties announced Wednesday that they will no longer allow indoor mask mandate exceptions for small settings like college and fitness classes in which everyone is fully vaccinated.

The four counties — along with the city of Berkeley, which operates its own public health department — said that their local indoor mask requirements will no longer have exceptions as of 12:01 a.m. Thursday.

Health officials in the five jurisdictions cited rising local case counts and the emergence of the highly contagious omicron variant as reasons to align with the state’s blanket indoor mask mandate, which runs through at least Jan. 15.

“The omicron variant requires us to use all the tools at hand to reduce the chance of transmission,” Berkeley Health Officer Dr. Lisa Hernandez said. “Masks are more important than ever to minimize the spread of COVID to our most medically vulnerable community members.”

Masks have been required indoors, regardless of vaccination status, in Berkeley and seven Bay Area counties, including Marin, San Francisco, Sonoma and Alameda, since early August amid the onset of the delta variant.

In early October, the four counties, the city of Berkeley and Contra Costa County allowed fully vaccinated people to remove their masks indoors in small settings that are not open to the general public like offices, fitness classes, occupational vehicles, religious gatherings and college classes.

Contra Costa County rescinded its masking exceptions on Tuesday.

Health officials across the region touted lower case rates when making those exceptions to their local masking orders in early October.

On Wednesday, officials in multiple counties said their case rates are reaching their highest levels in months.

According to Marin County, 338 new cases of COVID-19 were reported on Tuesday, more than 100 cases higher than the county’s previous highest one-day case count.

Marin County Public Health Officer Dr. Matt Willis said the region’s surge in cases tied to omicron necessitated a response.

“The mask exemption for certain settings was a pre-omicron policy,” Willis said in a statement. “This variant behaves differently, and the risk of infection in a room full of vaccinated people who are unmasked is much higher now.”

In addition to rescinding its mask mandate exemptions, San Francisco announced that it will formally align with the state’s requirement that workers in health care settings get a COVID-19 booster vaccination by Feb. 1, 2022, if they are eligible.

The city will also require that workers in high-risk settings, who are not covered by the state’s booster requirement, get a booster by Feb. 1 as well.

“As COVID-19 becomes endemic, we need to ensure everyone eligible gets vaccinated and boosted, we sustain our hospital capacity, and protect the most vulnerable — these updates to the Health Order help us achieve that,” San Francisco Director of Public Health Dr. Grant Colfax said in a statement.

Health officials in all five jurisdictions called on residents to get vaccinated against the virus if they have yet to do so, or to get a booster dose if they are eligible.

Booster vaccines are recommended for people age 16 and up who got their second Pfizer or Moderna vaccine dose at least six months ago or those who got their single Johnson & Johnson vaccine at least two months ago.