State Public Health Officer Order of January 5, 20212
California Department of Public Health - January 5, 2022
Guidance For the Use of Masks
The COVID-19 vaccines remain effective in preventing serious disease, hospitalization, and death from the SARS-CoV-2 virus. Unvaccinated persons are more likely to get infected and spread the virus which is transmitted through the air and concentrates indoors. To ensure that we collectively protect the health and well-being of all Californians; keep schools open for in-person instruction; and allow California’s economy to remain open and thrive, the California Department of Public Health (CDPH) is requiring masks to be worn in all indoor public settings, irrespective of vaccine status, until February 15, 2022. This requirement will be updated as CDPH continues to assess conditions on an ongoing basis.
This measure brings an added layer of mitigation as the Omicron variant, a Variant of Concern as labeled by the World Health Organization, continues to increase in prevalence across California, the United States, and the world and spreads much more easily than the original SARS-CoV-2 virus and the Delta variant.
Over the last two weeks, the statewide seven-day average case rate has increased by more than sixfold and hospitalizations have doubled. While the percentage of Californians fully vaccinated and boosted continues to increase, we continue to have areas of the state where vaccine coverage is low, putting individuals and communities at greater risk for COVID-19. Given the current hospital census, which is over capacity, the surge in cases and hospitalizations has materially impacted California’s health care delivery system within many regions of the state. Staffing levels are also increasingly impacted by COVID-19 transmission in many critical sectors.
As noted in the Science Brief by the Centers for Disease Control and Prevention (CDC) updated in December 2021, at least ten studies have confirmed the benefit of universal masking in community level analyses: in a unified hospital system, a German city, two U.S. states,,  a panel of 15 U.S. states and Washington, D.C.,,  as well as both Canada and the U.S., ,  nationally. Each analysis demonstrated that, following directives for universal masking, new infections fell significantly. Two of these studies,  and an additional analysis of data from 200 countries that included the U.S. also demonstrated reductions in mortality. Another 10-site study showed reductions in hospitalization growth rates following mask mandate implementation.
Implementing a universal masking requirement not only has proven to decrease the rate of infections but is able to slow community transmission. A series of cross-sectional surveys in the U.S. suggested that a 10% increase in self-reported mask wearing tripled the likelihood of slowing community transmission.
The masking requirement in California schools has allowed us to keep schools open when compared to other parts of the country. California accounts for roughly 12% of all U.S. students, but only 1% of COVID-19 related school closures. Nationally during the Delta surge in July and August 2021, jurisdictions without mask requirements in schools experienced larger increases in pediatric case rates, and school outbreaks were 3.5 times more likely in areas without school mask requirements., 
In workplaces, employers are subject to the Cal/OSHA COVID-19 Emergency Temporary Standards (ETS) or in some workplaces the Cal/OSHA Aerosol Transmissible Diseases (ATD) Standard and should consult those regulations for additional applicable requirements.
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