A COVID-19 vaccine clinic at the Bay Cities FC community appreciation event on June 19, 2021 at Sequoia High School, Redwood City, Calif. (Photo courtesy of Don Kianian/Bay Cities FC)

COVID-19 transmission levels remain high in San Mateo County, local health officials said Tuesday, and are likely to remain at a sustained level in the coming weeks.

Speaking to the county’s Board of Supervisors, officials with San Mateo County Health said the emergence of subvariants of the already highly contagious omicron variant are keeping both local and statewide transmission levels high.

The most recent subvariants of note, BA.4 and BA.5, are now the dominant strains of the virus in California and are estimated to be far more contagious than previous strains because of their apparent ability to evade antibody responses in those who have completed their initial vaccination series or been previously affected, according to researchers at Harvard Medical School.

While vaccination does continue to provide high protection levels against the virus’ worst outcomes, the existing omicron variants are likely to keep COVID transmission levels at a high level deeper into the summer, according to Marc Meulman, SMC Health’s director of public health, policy and planning.

“What we’re finding is that as these subvariants come along, one will overtake the previous because, essentially, they are more infectious,” he said.

Meulman also noted that, for now, the emerging subvariants are not causing serious illness in San Mateo County at similar rates to previous variants.

As such, COVID-related hospitalizations have remained relatively low and stable since late May, according to SMC Health Chief Louise Rogers, holding at a census between 30 and 50 patients.

That level of hospitalization, and even fewer patients in intensive care due to the virus, has kept local hospitals and medical centers from becoming overwhelmed with patients for the time being, she said.

Rogers and Meulman suggested that hospitalization levels will be the barometer for the foreseeable future to determine whether the county sees sustained levels of high transmission or a sudden spike in new cases.

That’s due in large part to the prevalence of rapid at-home COVID tests, they said, which are very effective at confirming infections among symptomatic people.

Those test results, however, are often not reported to the county, making it difficult to determine the true level of transmission from up-to-date case counts alone.

“We’ve had some big events that involve people gathering that might lead to higher numbers,” Rogers said, pointing to the Fourth of July.

“So we wouldn’t be surprised to see those numbers increase, but the main message is that we’re not concerned about the hospital capacity and also we see that people’s experience of the virus increasingly is not of severe disease if they are vaccinated,” she said.

The officials urged residents who have yet to do so to get vaccinated and, if eligible, at least one booster dose to protect against becoming seriously ill or dying.

They also advised that residents continue to wear masks indoors, although it is not a requirement in most public spaces.

As of Monday, 84 percent of San Mateo County residents have completed their initial vaccination series, while 62 percent of those aged 5 and up have received a booster dose.

Information about the virus can be found at https://www.smchealth.org/coronavirus.