BERKELEY (CBS SF) – Officials from San Francisco, Alameda and Marin counties announced Wednesday that they are requiring everyone to wear masks in indoor public settings in order to stem off the surge of COVID-19 cases across the country due to the spread of the Omicron variant.

The mandates, which follow recommendations from the California Department of Public Health (CDPH), go into effect at 12:01 a.m. Thursday in both counties. The mandates apply to everyone, regardless of vaccination status.

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“We have learned that Omicron can spread even among the vaccinated and those who had prior COVID infection,” said Dr. Nicholas Moss, Alameda County Health Officer, in a press release. “Masks work and are a critical layer of safety for everyone this winter.”

Berkeley, a city in Alameda County with its own health department, also instituted a mask mandate for public indoor spaces.

UCSF Infectious Disease Specialist Dr. Peter Chin-Hong said omicron is believed to be at least four times more transmissible then the delta variant. Chin-Hong told KPIX 5 we won’t get the complete picture of how bad the omicron surge will be until travelers return to the Bay Area after the holidays.

“The virus stays in the air like dandelions and people think omicron is exactly like that. It kind of lingers in the air and that’s why indoors is so risky and that’s why it so transmissible,” Chin-Hong told KPIX 5.

With omicron, cases are skyrocketing throughout the state, with a positivity rate above 11%. While the variant is infecting those that have been vaccinated, the California Department of Public Health says many of the severe cases are among the unvaccinated population.

People who talked to KPIX 5 weighed in on the resumption of universal masking indoors.

“I’m for the mandate. This is your life!” said Orinda resident Ben Chan.

“I also understand the fatigue people have and they’re sort of throwing up their hands. And I’ve met a lot of people who say, ‘Well if it happens, it happens,'” said Berkeley resident Catharine Trobridge.

“I’m not excited by it but I’m definitely going to follow it if that means someone doesn’t have to be hospitalized,” said Kiran Drish.

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Along with requiring masks despite vaccination status, San Francisco also made COVID-19 vaccination booster shots mandatory for workers in healthcare and high-risk settings. Employees in those fields must receive a booster shot by Feb. 1 of next year, which is also when the city will require staff at “indoor mega events.”

The highly transmissible Omicron variant recently spread quickly in both counties. Alameda County noted that its daily case rate is 18.7 per 100,000 residents and rising. Marin County noted that since the first case of the Omicron variant was discovered on Dec. 17, average daily COVID-19 case counts tripled – 338 new cases on Dec. 28 alone. In San Francisco, the 7-day average COVID-19 case rate was 398 as of Dec. 21, surpassing the peak average during the Delta surge, and data from the past week shows the rate continuing to increase.

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“When we see numbers like this, it’s time to respond,” said Dr. Matt Willis, Marin County Public Health Officer, in a press release. “The mask exemption for certain settings was a pre-Omicron policy. This variant behaves differently, and the risk of infection in a room full of vaccinated people who are unmasked is much higher now.”

Marin County noted that while COVID cases are increasing, the hospitalizations for COVID patients remain stable. Officials said the low rate is due to 92.1% of Marin’s population aged 5 and over is vaccinated.

Marin’s mask mandate is expected to last until Jan. 15 of next year. Alameda County did not provide an expiration date for its mandate.

Both counties recommended residents get vaccinated and boosted. They also suggested locals stay home if positive, symptomatic, or unvaccinated/not boosted and exposed, and for those to get tested if exposed, symptomatic, and before and after gathering and traveling.

“Omicron may be more transmissible, but we have the tools to prevent infection,” said Moss. “Because even a mild infection in a vaccinated person may be passed on to someone who could become hospitalized, we must take every precaution this winter.”

“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,” said Dr. Grant Colfax, San Francisco Director of Public Health.

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Kenny Choi and Andrea Nakano contributed to this report.