Flu hospitalizations in San Diego County hit 58 in a single week, more than 11 times the five recorded during the same period last year.

San Diego County's updated respiratory virus surveillance report, released Friday, Oct. 9, shows influenza test positivity at 8.0% for the week ending Saturday, Oct. 3. That compares to 0.7% during the same week of the 2025-26 season and a prior-years average of 1.0%.

Eight flu deaths had been reported through the week ending Oct. 3. At the same point last season, the county had recorded two.

The report also carries a new feature: two-week hospitalization forecasts for flu, COVID-19 and respiratory syncytial virus (RSV), built with UC San Diego's Resilient Shield project. The forecasting charts project flu hospitalizations trending upward through the week ending Oct. 10.

"It is vital that if you haven't gotten the flu shot or if you've been thinking about it to make the appointment or walk in as soon as possible," San Diego County Public Health Officer Sayone Thihalolipavan said in the Oct. 9 report. "The vaccine looks like it will be highly effective against the strain of flu now circulating."

UCSD connection

Resilient Shield is a CDC-funded initiative led by Eliah Aronoff-Spencer, a professor of medicine at UC San Diego School of Medicine. It is one of 13 core facilities in the CDC's Insight Net, a national outbreak and disease modeling network. The coalition includes researchers from UCLA, UCSF, Los Alamos National Laboratory, MIT and other institutions.

The partnership's first assignment was a flu-tracking request from Seema Shah, medical director of County Epidemiology and Immunization Services. That effort was co-led by Resilient Shield co-principal investigator Ruy Ribeiro at Los Alamos National Laboratory, according to a UC San Diego report on the project published in August.

The same partnership previously built an interactive dashboard tracking the Tijuana River Valley sewage crisis and has helped guide county surveillance of the New World Screwworm threat.

Vaccination lags

Only 10.2% of county residents, 336,490 people, had received a flu vaccine as of Oct. 3. That rate lags well behind. Full-season vaccination rates in recent years have reached 30.8% to 32.0%.

County health officials recommend vaccination by Halloween. The flu vaccine is covered by insurance and available at county public health clinics for uninsured residents.

COVID-19 test positivity stood at 8.1% for the same week but was decreasing. RSV positivity was 0.9% and stable.

The county's surveillance report is published weekly and available as a downloadable PDF.