California health officials say COVID is now peaking harder in summer than in winter, and they are seeing that shift again as activity rises in 2026. Dr. Erica Pan said the state's summer wave was much higher in 2025 than it was during the winter, a pattern that has changed how doctors and public health officials are thinking about the virus.
The timing matters because people are searching for answers while the U.S. Centers for Disease Control and Prevention says COVID-19 is growing or likely growing in 43 states. California is one of only four states where wastewater levels are considered moderate or high, a sign that the summer COVID surge in the United States is not just a statistical blip but a live public health problem.
The numbers back up the concern. Pan said California's summer peak in 2025 was far above the winter level, and national emergency department visits for COVID-related illness reached 1.7% last summer in late August, compared with a winter peak of 1%. In California, the gap was even wider: summer visits peaked at 2.1%, while winter maxed out at around 0.2%.
Peter Chin-Hong of UC San Francisco said the shift began in 2024, when cases, wastewater and hospitalizations jumped sharply in summer and even dwarfed the winter wave. He said that pattern continued in 2025, with more summer cases than winter cases, and pointed to FLiRT in 2024 and Nimbus and Stratus in 2025 as possible drivers of the seasonal change.
That explanation is still incomplete. It is not entirely clear why recent summers have been more active for COVID than winters, even as flu and respiratory syncytial virus usually peak in the colder months. Winter COVID waves were also much deadlier in the early years of the pandemic, when weekly deaths spiked at more than 15,000 around Labor Day in 2021 and climbed again to more than 21,000 in late January, a reminder that the virus has changed without becoming harmless.
Pan said people who have not gotten the 2025-2026 vaccines should still do so because the summer surge is already building. The question for the rest of the season is not whether COVID has a summer pattern now in California, but whether 2026 becomes another year when summer outpaces winter again.
