Mutated H3N2 variant raises flu hospitalizations in San Francisco

California health officials confirmed on Jan. 13 that a mutated H3N2 subclade is circulating in the state and that flu-related hospitalizations have reached seasonal highs. The variant, widely described in coverage as a "super flu" variant, has coincided with rising test positivity across the region and increased demand on hospital wards.

Infectious-disease experts, including clinicians at UCSF, note the current H3N2 strain is not a perfect match for this season’s vaccine, but they emphasize that vaccination still substantially reduces the risk of severe illness and hospitalization. Public-health officials are urging San Francisco residents to use the tools that blunt severe outcomes: get vaccinated, test when symptomatic, and for people at higher risk seek early antiviral treatment.

Local hospitals are responding to the uptick in admissions while maintaining routine services. Emergency departments in the county have seen heavier patient loads typical of a winter surge, and clinics that serve older adults, people with chronic conditions, and congregate-living settings are advising heightened vigilance. The combination of a mutated H3N2 subclade and increased respiratory mixing on Muni, BART and in workplace settings has amplified transmission opportunities this month.

Testing remains a central element of the response. Rapid tests can confirm infection quickly so people can isolate and, when appropriate, seek antiviral medication within the window where those drugs work best. Public-health guidance highlights that early treatment is most beneficial for older adults, pregnant people, the immunocompromised and those with chronic health problems — the same groups that tend to experience the worst complications from influenza.

For San Francisco families and employers, the immediate implications are practical. Vaccination clinics, pharmacy shots and workplace leave policies can reduce onward spread; staying home while sick, masking in crowded indoor spaces when cases are high, and testing before visiting vulnerable people reduce risk. Health systems are balancing surge capacity with ongoing care, so minimizing preventable hospitalizations helps preserve services for everyone.

The takeaway? Think of this season as a reminder to use every layer of protection available: get your shot even if it’s not a perfect match, test quickly if you have symptoms, and seek antivirals early if you’re in a high-risk group. Our two cents? A little extra caution now — vaccine, test, treat — keeps San Francisco’s hospitals and neighborhoods healthier through the peak.