COVID-19 is rising in the Bay Area, on par with a summertime trend seen in prior years, and public health officials are urging residents to take precautions.

The percentage of positive tests for the virus in the Bay Area rose from low levels in July (3.75%) to moderate levels (9.34%) in mid-August, the most recent California Department of Public Health data shows. A high level would be between 11 and 16%, the classification the region hit by this time in 2025. Another measure of the virus’ spread — concentrations in wastewater at treatment plants — shows high levels in Vallejo, San Francisco and parts of Silicon Valley. The data does show some good news: Hospitalizations due to COVID-19 are much lower regionwide than the past two summers so far.

Here’s how experts explain the trend and recommend staying healthy.

Q: Why does COVID-19 spread more in the summer in the Bay Area?

A: Two leading experts on infectious diseases in the Bay Area, Yvonne Maldonado of Stanford and Peter Chin-Hong of UC San Francisco, both said that’s a mystery. “We don’t have a good understanding in general of why viruses and bacteria have seasonality,” Maldonado said.

Q: Why are hospitalizations low so far during this summertime surge?

A: COVID-19 can infect a person repeatedly, and that’s often the case. More people have been exposed to the virus with each passing year. “Just about everybody has either had infection, or vaccination, or both,” Maldonado said. “So there’s a lot of immunity.”

Q: Is the virus still a risk to the public?

A: Adults 65 and older, young children and people with compromised immune systems due to other chronic illnesses, like cancers, are at heightened risk. For many otherwise healthy people, infection by COVID-19 might feel like the common cold, Chin-Hong said in an interview last month.

Q: Who should get vaccinated, and is the 2025-26 shot still effective?

A: Vaccination reduces the likelihood of a serious illness, hospitalization and death. The California Department of Public Health recommends the vaccine for everyone 6 months and older. For those at higher risk, it recommends “anyone who hasn’t received a dose of 2025-2026 COVID-19 vaccine or is due for a second dose get vaccinated now as we’re seeing increases in infections.”

The COVID-19 vaccine has been updated annually to provide protection against new mutations. That hasn’t happened since early 2025 when the Stratus strain of the virus cropped up, Maldonado said. Public health officials continue to recommend the 2025-26 vaccine. The new vaccine will be available in the Bay Area this fall, according to Kaiser Permanente and the San Francisco Department of Public Health.

Q: Should I wear a mask?

A: Masks are “especially helpful” at reducing exposure to the virus, according to the state public health department. Residents who are high-risk or find themselves indoors or in a crowded space should mask up, the agency said. People should also wash their hands often. “Infection can spread if you touch something contaminated and then touch your face before washing your hands,” it said.

Q: What do I do if I get sick?

A: Stay at home, the health department says. Common symptoms of COVID-19 are a sore throat, fever and cough. To treat a mild or moderate case that’s not serious enough to go to a hospital, the antiviral medication Paxlovid is available by prescription for higher-risk adults. To be effective, the medication should be taken within five days of symptoms developing.

Q: What else should people consider if they get vaccinated? What about the flu shot?

A: Updated shots for influenza, which mutates quickly, will be available for Kaiser Permanente patients in September, the hospital network says on its website. Maldonado encouraged residents to seek out flu shots when they’re available. “Flu season will show up before you know it,” she said, “and we really need to get people vaccinated before that happens.”