COVID cases are rising quickly among S.F. teenagers. What’s going on?

"There are probably multiple factors contributing to the rise in cases among teenagers," said Dr. Anne Liu, a Stanford pediatrician and infectious disease expert. "With the surge in cases in all age groups, teens are going to have more cases as they pick it up from family members and friends. Even vaccinated teens are at risk for picking up omicron, even if they are greatly protected against severe disease."

When asked for comment, the San Francisco Department of Public Health said they could not verify the findings, but were doing their best to vaccinate 12- 15-year-olds now that they are eligible for boosters.

The seven-day average of new coronavirus cases in San Francisco reached a pandemic high of 1,661 on Thursday — about 255 new cases per 100,000 residents, according to the city's health department. The highly infectious omicron variant, which is now the dominant strain in the region, is causing enormous spikes everywhere — more than 100,000 new cases are being reported every day in the state, and more than 15,000 daily in the Bay Area.

California does not break down its case rates by the same age brackets as San Francisco. Instead, its public data groups all people under 18 into a single category. The state does not appear to be experiencing the same disproportionate surge in its youth as San Francisco. Case rates for people under 18 statewide are currently lower than that of the population as a whole.

Dr. Naomi Bardach, associate professor of pediatrics at UCSF, said that social behavior over the winter break is also likely a factor in the surge — which can help explain why 12- to 17-year-olds are seeing higher case rates than the 5- to 11-year-old age group.

"Kids were potentially mixing more in that older age group than in those younger age groups," Bardach said.

Dr. Stephanie Chiang, a pediatrician who practices at Sutter's Palo Alto Medical Foundation Fremont Urgent Care, said the sharp increase in cases among adolescents — especially among the 12 to 15 age group — is partly because they were only recently approved to receive booster shots and many have not yet had a chance to schedule them, leaving them more vulnerable to infection.

"Many of them started getting their initial vaccine series in May and the recommendation is to get boosted after five months," she said. "A lot of them are unprotected from that standpoint."

Hospitalizations among teens remain stable.

The experts think lifestyle may also play a role in spreading the virus, especially with omicron.

"Many teens have resumed their normal activities including school, sports, music and clubs in settings that bring people together unmasked," said Liu. "Many winter sports like basketball are largely played indoors."

Chiang recommends that families temporarily pause indoor sports through the winter surge. She also said parents should make sure their children upgrade their masks to high quality KN95s or KF94s, eat lunch outdoors at school, and test frequently. They should stay home if they have any symptoms.

"I think it's important for their health and well-being that they're back in school," she said. "That's where you have to balance all the factors."

Bardach said the high case rates among adolescents in San Francisco also likely reflects proactiveness by kids and their parents about getting tested as the school year resumes.

"We actually saw this (during) delta," Bardach said. "When kids were going back to school there was an apparent spike in kids (case rates), but it was actually because of an added safety layer in schools."

The San Francisco Unified School District offers a testing program for its students, with multiple sites operating at various schools along with mobile services; the district recently distributed 60,000 at-home test kits to students (although some schools have seen significant testing shortages, as the city has overall).

Many of the city's private schools also have significant testing resources. Kids are getting tested out of school, too: Bardach said her pediatric clinic has seen testing demand increase recently.

Coupled with parents' concerns over the omicron spike, that demand may have contributed to a surge in testing among young people that has made their share of cases look higher than other city residents.

"As the pandemic drags on and we are seeing rises in mental health concerns among teens, some families are making some trade-offs to allow teens more normalcy in their social lives," Liu said. "Although testing might be picking up more cases, we know there is a real increase in COVID in the community because the test positivity rate is high. We can't blame this on increased testing."

Susie Neilson and Aidin Vaziri are San Francisco Chronicle staff writers. Email: [email protected] , [email protected]