Flu vaccine uptake low in Southern Hemisphere, study finds
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Key takeaways:
- Vaccination significantly reduced influenza hospitalizations in the Southern Hemisphere this year.
- Uptake was poor, however, and below pre-COVID-19 levels.
Vaccination reduced influenza-related hospitalizations by around one-third in the Southern Hemisphere this year, according to interim data published Thursday by the CDC.
But researchers also found that influenza vaccine uptake was poor, remaining below pre-COVID-19 levels.
“This finding is consistent with post-pandemic declines in vaccination coverage across the Americas associated with vaccine misinformation, hesitancy, and disruptions in routine immunization services, prevalent during the COVID-19 pandemic,” the researchers wrote in MMWR.
According to the new report, just 21.3% of people in five South American countries — Argentina, Brazil, Chile, Paraguay and Uruguay — received an influenza vaccine this season. Uptake was similarly poor across high-risk subgroups, including older adults (29.3%), young children (19.4%) and patients with comorbidities (14.5%).
Still, the researchers wrote, people who did receive a vaccine were at a significantly lower risk for serious illness. They calculated vaccination to be 34.5% effective at preventing influenza-related hospitalizations, down from around 50% last year.
Influenza season, which is just getting underway in the Northern Hemisphere, typically occurs between April and September in the Southern Hemisphere.
The United States switched to trivalent formulations for all of its influenza vaccines this season, removing an influenza B strain that has not circulated since the start of the COVID-19 pandemic.
Because the U.S. is using the same vaccine components that were in the Southern Hemisphere’s vaccine, the new vaccine estimates from below the equator could indicate how effective vaccination will be in the U.S. if the same viruses circulate, according to the researchers.
They said the data support long-standing recommendations that everyone aged 6 months or older receive an influenza vaccine.
“Although Southern Hemisphere influenza vaccine effectiveness is not necessarily predictive of Northern Hemisphere vaccine effectiveness, it can help the Northern Hemisphere plan contingencies for vaccination demand and use,” they wrote.
References:
- CDC. South America’s 2023 flu vaccine cut risk of flu hospitalizations by about half. https://www.cdc.gov/flu/whats-new/2022-2023-south-america-flu-hospitalizations-half.html. Published Sept. 8, 2023. Accessed Oct. 3, 2024.
- FDA. Use of trivalent influenza vaccines for the 2024-2025 U.S. influenza season. https://www.fda.gov/vaccines-blood-biologics/lot-release/use-trivalent-influenza-vaccines-2024-2025-us-influenza-season. Last updated March 5, 2024. Accessed Oct. 3, 2024.
- WHO. Recommended composition of influenza virus vaccines for use in the 2024 southern hemisphere influenza season. https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2024-southern-hemisphere-influenza-season. Published Sept. 29, 2023. Accessed Oct. 3, 2024.
- Zeno EE, et al. MMWR Morb Mortal Wkly Rep. 2024;doi:10.15585/mmwr.mm7339a1_w.
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