A new study finds that flu shots were associated with moderate protection against the virus during the 2024-25 flu season.
People vaccinated against influenza that season were 40% less likely to test positive for flu than unvaccinated people, according to a study of more than 1.1 million Californians.
Adults aged 65 and older who tested positive for flu were 29% less likely to die of an influenza-related cause if they had received the vaccine, according to the study, published yesterday in JAMA Network Open. The study included flu-related deaths within 30 days of testing.
“These findings are consistent with protection against severe and fatal influenza among people vaccinated against influenza,” the study authors wrote.
A ‘high severity’ flu season
The analysis comes from a case-control study of people aged 6 months or older who were tested for influenza from October 1, 2024 to May 31, 2025, which was considered a “high severity” flu season, with the highest rate of influenza-associated hospitalizations in 24 years.
Flu caused an estimated 610,000 to 1.3 million hospitalizations that season, along with 27,000 to 130,000 deaths, according to the study, led by the California Department of Public Health.
The flu killed 289 children that year, surpassing the previous record set during the 2009 to 2010 season, which was marked by the H1N1 flu epidemic.
Public health experts recommend annual flu shots to reduce the risk of illness, hospitalization, and death.