The mandate will go into effect at 12:01 a.m. Friday and will apply to most indoor public settings, including grocery stores and gyms.
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Students and staff at K-12 schools will not be required to wear masks under the order through the end of the 2021-2022 school year, according to the Alameda County Health Care Services Agency, but they will be required in all other settings for children including summer school and youth programs.
AC Transit has also reinstated the mask mandate as of Friday.
The order will not apply to the city of Berkeley, which operates as its own local health jurisdiction. A spokesperson for the city did not respond when asked whether Berkeley will align with the county.
"Rising COVID cases in Alameda County are now leading to more people being hospitalized and today's action reflects the seriousness of the moment," county Health Officer Dr. Nicholas Moss said in a statement. "We cannot ignore the data, and we can't predict when this wave may end."
VIDEO: Expert explains why mask mandates won't work at this stage in COVID pandemic
Expert explains why mask mandates won't work at this stage in COVID pandemic
Oakland Unified officials announced Thursday night it was reinstating its indoor mask mandate in wake of Alameda County's announcement. Officials say this will go into effect June 3 and people will be required to wear masks at all OUSD facilities.
Alameda County is the first county in the Bay Area to reinstate mask requirements in indoor public settings since February, when the state and most counties in the greater Bay Area lifted mask requirements that were implemented to combat the winter surge driven by the omicron variant.
Santa Clara County was the lone holdout among the 11 counties in the greater Bay Area, keeping its indoor mask requirement in place until March 2.
Health officials have urged a return to widespread masking in recent weeks amid a new surge in cases primarily spurred by the omicron subvariant BA.2.
According to Alameda County health officials, COVID cases began to rise in April and the daily number of reported cases has eclipsed the peak of last summer's wave driven by the delta variant.
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Local COVID hospitalizations have also risen to 102, as of Monday, after falling as low as 37 in early April.
COVID cases in general are largely undercounted, according to health officials, due to the wider availability of at-home tests that do not necessarily get reported to the county and infections that may remain asymptomatic and undetected.
"Putting our masks back on gives us the best opportunity to limit the impact of a prolonged wave on our communities," Moss said.
Doctor Monica Gandhi is an infectious disease expert at UCSF.
"Mandates, especially after vaccination, didn't seem to work," she said.
Dr. Gandhi says while she thinks masks are effective, data doesn't always show that mandates work.
She points to studies out of Southern California that show counties both with and without mandates had similar results in previous COVID waves.
"We have the tools, which are vaccines and therapeutics to combat it," said Gandhi.
Alameda health officials say there's no timeline for when the new mandate might end. But, they say they're hopeful it will be sooner rather than later.
"This is really intended to be a short term measure to try and get this wave under control. And we'll lift it as soon as we can," Moss said.
COVID information and resources for Alameda County can be found here.
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