SACRAMENTO, Calif. — Influenza vaccination provided moderate protection during the severe 2024-25 flu season, with people who received the shot 40% less likely to test positive for the virus compared to those who did not, according to a large new study of more than 1.1 million Californians.

The analysis, published in JAMA Network Open, offers fresh evidence of the vaccine's benefits amid one of the most intense flu seasons in recent memory, marked by record pediatric deaths and elevated hospitalizations nationwide.

Researchers from the California Department of Public Health examined data from individuals aged 6 months and older who were tested for influenza between Oct. 1, 2024, and May 31, 2025. The case-control study found clear associations between vaccination and reduced odds of both infection and severe outcomes.

"These findings are consistent with protection against severe and fatal influenza among people vaccinated against influenza," the study authors wrote.

For adults aged 65 and older who tested positive for flu, vaccination was linked to 29% lower odds of dying from an influenza-related cause within 30 days of testing. This protection against mortality underscores the vaccine's role in safeguarding the most vulnerable populations during peak transmission periods.

The 2024-25 season was classified as high severity, with the highest rate of influenza-associated hospitalizations in 24 years. Nationwide estimates cited in the study pointed to between 610,000 and 1.3 million hospitalizations and 27,000 to 130,000 deaths. Tragically, the flu claimed the lives of 289 children, surpassing the previous record from the 2009-2010 H1N1 pandemic season.

Public health officials have long emphasized annual vaccination as the primary tool for mitigating flu's impact. The Centers........

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