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Prevention Strategies


COVID-19 Prevention Strategies

Virus Levels & Exposure Risk in San Mateo County

While there are many ways to quantify COVID-19 risk in San Mateo County, including the CDC’s Community Level, which measure impacts on local health care systems, County Health stresses that there is still significant community transmission of COVID in San Mateo County. Virus levels are 2-5 times higher than the low levels of March 2022. While cases are gradually decreasing, the Omicron variants remain prevalent and residents face a risk of exposure.

Virus transmission levels are estimated by County Health by reviewing many sources, including data from local laboratories, hospitals, PCR tests, schools, and wastewater surveillance.

The number of reported cases severely underestimates the level of virus in San Mateo County because so many people use rapid antigen tests (that are not reported to health departments) and few use PCR tests (which are reported).

To prevent infections and severe disease in San Mateo County and the Bay Area region, it’s important to be current with vaccinations and boosters (including the new, updated booster), get tested if you have symptoms, and wear a mask to prevent exposure and spread, especially if you have symptoms, a positive test, or a known exposure to someone with COVID-19.

The California Department of Public Health and San Mateo County Health recommend best practices to protect individuals and communities.

Individual Prevention 

  • Get the updated, bivalent booster to prevent infections from the Omicron strain circulating in San Mateo County
  • The best way to prevent infection is to wear a high-quality mask (N95, K95) in indoor public spaces, such as grocery stores
  • Maintain improved ventilation throughout indoor spaces when possible and avoid closed spaces with poor ventilation
  • Stay home if you feel sick and get tested right away
  • Follow the California Department of Public Health (CDPH) guidance on isolation and quarantine 
  • If you are immunocompromised or at high risk for severe disease, consider wearing a mask in indoor public spaces, have a plan for rapid testing (e.g. access to at-home tests), and talk to your healthcare provider about whether you are a candidate for treatments like oral antivirals, pre-exposure prophylaxis (PrEP), and monoclonal antibodies 

Community Prevention

  • Distribute and administer vaccines to achieve high community vaccination coverage and ensure health equity 
  • Maintain improved ventilation in public indoor spaces 
  • Ensure access to testing, including through point-of-care and at-home tests for all people 
  • Communicate with organizations and places that serve people who are immunocompromised or at high risk for severe disease to ensure they know how to get rapid testing 
  • Ensure access and equity in vaccination, testing, treatment, community outreach, support services for disproportionately affected populations
  • Advise businesses, venue operators, event hosts and other organizations to consider requiring patrons to wear masks inside their facilities

Importance of Indoor Ventilation 

Proper indoor ventilation while gathering inside reduces the spread of COVID-19. Proper ventilation includes opening windows and doors to bring fresh air in or using an air filtration system (please check air quality during fire season prior to opening windows and doors). Using an air filtration system indoors can reduce COVID-19 particles in the air by 72% after an hour of use. Leaving a single window open for an hour can reduce COVID-19 particles by 44%. Practicing these simple steps when gathering indoors, can significantly reduce the risk of spreading COVID-19.  For further guidance on indoor ventilation from the CDC, visit Improving Ventilation in Your Home.

CDC Indoor Ventilation Tips

The risk of getting COVID-19 varies according to individual susceptibility and the number of virus particles to which a person is exposed. The fewer virus particles in the air, the better. Adjusting ventilation settings can reduce the number of particles and infections.

Bring as much fresh air into your home as possible.

  • Open doors and windows as much as you can to bring in fresh, outdoor air, if it’s safe to do so.
  • If opening windows or doors is unsafe, consider other approaches for reducing virus particles in the air, such as using air filtration and bathroom and stove exhaust fans.

Filter the air in your home.

  • Set the fan to the “on” position instead of “auto” when you have visitors.
  • Change your filter every 3 months or according to manufacturer’s instructions

Use fans to improve air flow.

  • Place a fan as close as possible to an open window blowing outside, which helps get rid of virus particles.
  • Point fans away from people.

Consider using a portable air cleaner, particularly when you have guests.