COVID-19 is showing ‘stirrings of a summer surge’ in California

Travel season is in full swing, and so is COVID-19 transmission, municipal wastewater data suggests. 

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According to recent data from WastewaterSCAN, which monitors the rates of several viruses in municipal wastewater, San Francisco, Palo Alto and San Jose are grappling with high rates of COVID. Meanwhile, the virus has a moderate presence in Novato, Napa, Sunnyvale and Fremont. 

“I think now we’re seeing the stirrings of a summer surge,” Dr. Matt Willis, a former health officer for Marin County, told SFGATE over the phone Tuesday. 

“The big picture is that we’re still developing our relationship with this virus in terms of its periodicity and its rhythms with human populations” since it’s still so new, he explained.

However, “we haven’t had a year ever where there hasn’t been significant COVID activity in the summertime,” he continued, adding that while rates are rising, the Bay Area still isn’t experiencing a surge just yet. WastewaterSCAN’s website also says that while the virus has been on the upswing in San Francisco over the past 21 days, rates in the city this year are much lower compared with rates last year. 

“In California, we’re starting to see that our summer waves are more serious than winter waves,” Willis told SFGATE, adding that he won’t be surprised if masks will eventually be recommended indoors. 

Nationwide, the Northeast is seeing moderate levels, and the South is seeing high levels of the virus.

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Overall, COVID levels in the Bay Area have been very low since last fall, which is “the longest interval ever since the start of the pandemic,” Willis said. From an immunity standpoint, that also means that people might be more susceptible to infection since so much time has passed.

Luckily, there’s no evidence showing that the dominant variant, XFG.1.1, “is materially different in terms of infectivity and symptoms that it causes,” Willis continued. XFG, or “stratus,” which shares traits of omicron, was detected last year and has since spread across multiple regions of the U.S., a 2026 study published in the Journal of Epidemiology and Global Health says. 

Overall, levels are still low, Willis said, “but for those who have been holding off on vaccines since last fall and who are at risk, this is a good time to go ahead and get that vaccine.”