California sees COVID-19 cases rise in summer as winter activity wanes
Health officials report that COVID-19 infections, hospitalizations and wastewater levels are higher in California during the summer than in winter, prompting renewed vaccination recommendations.
California health officials say the state is experiencing a shift in COVID-19 activity, with summer months now showing higher case numbers and hospitalizations than the traditional winter peak. The U.S. Centers for Disease Control and Prevention reports that COVID-19 is growing or likely growing in 43 states, including California, and that the state is one of only four where wastewater monitoring shows moderate or high viral activity.
"Our summer peak was much higher in 2025 than it was in the winter," said Dr. Erica Pan, director of the California Department of Public Health. She added that vaccination remains effective and is strongly recommended for those who have not received the 2025-26 booster.
National data show a similar pattern, 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 note that the change may be linked to newer subvariants, such as the 2024 FLiRT and the 2025 Nimbus and Stratus strains, although the exact reasons remain uncertain. Dr. Peter Chin-Hong of UC San Francisco observed that large summer increases began in 2024 and continued into 2025, overtaking winter surges.
The California Department of Public Health advises residents, especially those 65 and older, immunocompromised individuals, pregnant women and young children, to receive a second COVID-19 vaccine dose six months after the first. The department also recommends the 2025-26 vaccine for high-risk groups and anyone who has not yet been vaccinated with the latest formulation.
Recent test-positivity rates have risen, with the San Francisco Bay Area reporting 7% positivity for the week ending Aug. 1, up from 2.7% a month earlier. Los Angeles County recorded 4.25% and Orange County 6.5% for the same period. Hospitalization rates remain lower than in previous summers, at 0.84 per 100,000 residents, but officials forecast a moderate increase later this summer and early fall.
Nationally, COVID-19 deaths have declined from pandemic peaks, with 20,685 deaths recorded in 2025. California reported 1,813 COVID-related deaths that year.
In related news, the FDA approved an mRNA-based flu vaccine for adults 50 and older, which could speed the development of future flu shots against emerging strains.