COVID-19 is showing signs of an increase this summer in California

COVID-19 Transmission During Travel Season

As travel season picks up, data from municipal wastewater indicates that COVID-19 transmission is also rising.

Recent information from WastewaterSCAN, which tracks various viruses in municipal wastewater, reveals that cities like San Francisco, Palo Alto, and San Jose are facing elevated COVID-19 rates. In contrast, Novato, Napa, Sunnyvale, and Fremont are experiencing moderate levels of the virus.

“I think we might be witnessing the beginnings of a summer surge,” Dr. Matt Willis, a former health officer for Marin County, shared with SFGATE on Tuesday. He emphasized that our understanding of the virus’s behavior, particularly its interactions with human populations, is still evolving.

Despite the rising numbers, he pointed out, “We’ve never had a summer without significant COVID activity.” He noted that while the Bay Area’s rates are increasing, they are still lower this year compared to last. WastewaterSCAN indicates that San Francisco has observed a surge in the past 21 days, yet the current levels remain lower than those from the previous year.

Willis remarked, “In California, it seems our summer spikes might be more severe than those in winter.” He wouldn’t be surprised if indoor mask recommendations return.

Nationally, COVID-19 levels in the Northeast are moderate, while the South is seeing higher counts.

Willis mentioned that overall COVID levels in the Bay Area have remained quite low since last fall, marking “the longest stretch since the pandemic began.” This lengthy period could mean increased susceptibility to infection as immunity wanes.

Fortunately, the dominant variant, XFG.1.1, appears similar to previous strains in how easily it transmits and the symptoms it causes. This variant, known as “stratus,” emerged last year and has spread across numerous U.S. regions, according to a 2026 study published in the Journal of Epidemiology and Global Health.

While overall levels remain low, Willis suggested that for individuals who have delayed vaccination since last fall and are at risk, now might be the right time to get vaccinated.