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A study of over 1.1 million Californians found that flu shots reduced the likelihood of testing positive for influenza by 40%. Vaccinated seniors also had a 29% lower risk of flu-related death. The findings support vaccination as a key public health measure.
A new study published today in JAMA Network Open confirms that individuals who received flu shots during the 2024-25 season were 40% less likely to test positive for influenza than those unvaccinated, highlighting the vaccine’s effectiveness during a high-severity season.
The study analyzed data from more than 1.1 million Californians tested for influenza between October 1, 2024, and May 31, 2025. It found that vaccinated individuals had a 40% lower chance of testing positive for the flu compared to unvaccinated people. The season was characterized by high severity, with an estimated 610,000 to 1.3 million hospitalizations and up to 130,000 deaths, marking one of the deadliest seasons in recent years.
Additionally, among adults aged 65 and older who tested positive for influenza, those vaccinated were 29% less likely to die from influenza-related causes within 30 days of testing. The study authors noted that these findings are consistent with the vaccine’s role in reducing severe and fatal influenza outcomes, reinforcing public health recommendations for annual flu vaccination.
Impact of Flu Vaccination on Public Health Outcomes
The findings underscore the importance of annual flu vaccination as an effective measure to reduce both infection rates and severe outcomes, including hospitalization and death. This evidence supports ongoing vaccination campaigns and could influence public health policies to increase vaccination coverage, especially during high-severity seasons.
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High Severity Season and Vaccination Effectiveness Data
The 2024-25 flu season was classified as high severity, with the highest rate of influenza-associated hospitalizations in 24 years. The season saw an estimated 610,000 to 1.3 million hospitalizations and up to 130,000 deaths, surpassing previous records. The study reflects a broad effort to assess vaccine effectiveness during this challenging period, providing critical data on the protective benefits of flu vaccination.
“These findings are consistent with protection against severe and fatal influenza among people vaccinated against influenza.”
— study authors
Unanswered Questions About Long-Term and Broader Impact
While the study confirms the effectiveness of flu vaccines during this season, it is not yet clear how these findings translate to other seasons or different populations. Further research is needed to understand long-term protection and the impact of vaccination on influenza transmission dynamics.
Next Steps for Public Health and Vaccine Policy
Health authorities are expected to analyze these findings to reinforce vaccination campaigns for upcoming flu seasons. Additional studies may focus on optimizing vaccine formulations and coverage to further reduce influenza burden. Public health agencies will likely continue to monitor vaccine effectiveness and influenza activity in real-time.
Key Questions
How effective are flu vaccines overall?
Flu vaccines typically reduce the risk of testing positive for influenza by about 40% during high-severity seasons, according to recent studies. They also significantly lower the risk of severe illness and death, especially among vulnerable populations.
Does vaccination prevent all cases of the flu?
No, flu vaccines do not prevent all cases, but they substantially decrease the likelihood of infection and severe outcomes. Effectiveness varies by season and population.
Are older adults protected by the flu vaccine?
Yes, older adults benefit from vaccination, with evidence showing a 29% reduction in flu-related deaths among those aged 65 and older during the 2024-25 season.
What is the significance of this study for public health?
This study reinforces the importance of annual flu vaccination as a key tool to reduce infection rates, hospitalizations, and fatalities, especially during severe seasons.
Will these findings influence future vaccination policies?
Likely yes. Public health officials may use this data to promote higher vaccination rates and improve vaccine strategies for upcoming flu seasons.
Source: Google Trends
