Dr. Matt Willis, Marin County's Public Health Officer, attends one of the first pop-up senior COVID-19 vaccination clinics, set up at the Exhibit Hall of the Marin County Civic Center in March 2021. (Photo courtesy County of Marin)

Officials in Marin County are again advising residents and visitors to wear high-quality masks as the BA.4 and BA.5 variants of omicron dominate the county’s COVID-19 samples.

On Thursday, the county said that the BA.2-related variants have shown high transmission rates over the last three months, with 90 percent of all COVID-19 infections being linked to them. These strains are also better able to evade the body’s immune response, county health officials said.

Marin County Public Health officials said they do not intend to institute a local mask mandate, however. Instead, the county is educating the community about the risks they face and the protection that high-quality masks can offer.

One in 20 residents of Marin County are currently infected with COVID-19, county officials said. That means the likelihood of being exposed to the virus in gatherings of people roughly breaks down this way: If the number of people present is 10, there is a 40 percent chance that at least one person is infected. In a gathering of 25 people, that percentage goes up to 72 percent. A group of 50 people means the likelihood of at least one person being infected there is at 92 percent. And in groups of 100, the likelihood is 98 percent that someone is infected.

Marin County Public Health Officer Matt Willis said wearing a good mask is a “simple step” to protect oneself and their loved ones. Willis notes that N95, KN95 or KF94 masks are superior to cloth masks when community case rates are high.

The county also recommends that all residents over the age of 50 obtain a second booster dose.

According to the Marin County COVID-19 dashboard data, 97 percent of eligible county residents have received their first dose of the vaccine, 90 percent completed that series, and nearly 65 percent have been boosted.