California sees COVID cases rise more in summer than winter, officials urge vaccination
Health officials in California report that COVID-19 activity is now higher in the summer than in winter and are recommending updated vaccinations for high-risk groups.
California health authorities say COVID-19 infections, wastewater detections and hospitalizations have been higher during the summer months than in winter for the past two years. The Centers for Disease Control and Prevention notes that the state is one of four where wastewater activity is classified as moderate or high, and COVID-19 is currently growing in 43 states, including California.
"Our summer peak was much higher in 2025 than it was in the winter," Dr. Erica Pan, director of the California Department of Public Health, told a briefing. She added that the vaccine for the 2025-26 season remains effective and is recommended for those who have not yet received it.
National data show a similar shift, with COVID-related emergency department visits reaching 1.7% of total visits in August, compared with 1% during the winter. In California, the summer share rose to 2.1% while the winter peak stayed around 0.2%.
Experts attribute the change to a combination of newer viral subvariants, such as the 2024 FLiRT and the 2025 Nimbus and Stratus strains, and increasing levels of vaccine-derived and natural immunity. "This past fall and winter marked a change in how the COVID waves have been coming, with very little activity," said Dr. Elizabeth Hudson of Kaiser Permanente Southern California.
The state continues to advise seniors, immunocompromised individuals, pregnant women and young children to receive the latest vaccine dose. "Anyone who hasn’t received a 2025-26 dose, or is due for the second dose, is encouraged to get vaccinated now, before the next COVID-19 surge," a slide in Dr. Pan’s presentation stated.
Hospitalization rates have risen modestly, with 0.84 admissions per 100,000 residents reported recently, down from 1.92 the previous year. Test positivity in the San Francisco Bay Area increased to 7% for the week ending Aug. 1, up from 2.7% a month earlier, while Los Angeles County reported a 4.25% positivity rate.
The California Department of Public Health projects a moderate increase in COVID-related hospital admissions later this summer and early fall, and continues to monitor wastewater and case trends.