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As the 2024-2025 flu season approaches in the Northern Hemisphere, U.S. health officials are raising concerns about the potential effectiveness of this year’s influenza vaccine. According to the Centers for Disease Control and Prevention (CDC), early reports from South America indicate that the flu vaccine used in the Southern Hemisphere might be less effective compared to last year’s vaccine, which could signal a similar trend in the United States.
The CDC’s data, drawn from five South American countries—Argentina, Brazil, Chile, Paraguay, and Uruguay—shows that this year’s flu vaccine reduced the risk of hospitalization for high-risk individuals by just 35%. This is a notable drop from the 51.9% effectiveness reported during the last flu season in the same region. These findings are based on a research network coordinated by the Pan American Health Organization.
Implications for the Northern Hemisphere
Since flu seasons in South America occur between April and September, they often serve as an early indicator for how influenza might spread and affect populations in the Northern Hemisphere, where flu season typically spans from October to April. The CDC warns that if similar flu viruses—particularly H1N1, H3N2, and influenza B (Victoria)—circulate in North America, vaccine efficacy might mirror the results seen in South America.
During the past flu season in North America, the CDC estimated that the vaccine was 41% to 44% effective in preventing flu-related hospitalizations among adults and 52% to 61% effective in children. These rates highlight the critical role of the flu vaccine, even with variable effectiveness, in reducing severe illness and preventing hospitalizations.
What to Expect from This Year’s Vaccine
For the 2024-2025 flu season, the U.S. is using trivalent vaccines that target the three main strains anticipated to circulate—H1N1, H3N2, and influenza B (Victoria). Despite the uncertainty regarding the vaccine’s effectiveness, health officials strongly recommend flu vaccinations for everyone aged 6 months and older. The flu shot remains the best defense against severe outcomes such as hospitalization and death, especially for high-risk groups, including older adults, young children, and individuals with underlying health conditions.
Flu’s Impact in the U.S.
Influenza continues to be a major public health challenge in the U.S. The CDC estimates that between October 2023 and April 2024, approximately 75 million people contracted the flu. Of those, 900,000 required hospitalization, and flu-related deaths ranged between 17,000 and 100,000. These figures underscore the importance of annual flu vaccination campaigns and ongoing public health efforts to mitigate the virus’s impact.
A Call for Vigilance
Though this year’s vaccine may not offer as high a level of protection as hoped, the CDC emphasizes that it is still crucial for people to get vaccinated. With flu season just around the corner, individuals are urged to take preventive steps, including receiving the flu vaccine and practicing good hygiene, to minimize the spread of the virus and protect vulnerable populations.
As the flu season progresses, health authorities will continue to monitor vaccine effectiveness and flu activity, adjusting recommendations as necessary to safeguard public health.
