The analysis, published Nov. 16, 2023, in Clinical Infectious Diseases, found the seasonal influenza vaccine was only 48 percent effective overall at reducing the risk of influenza-A-associated emergency department (ED) or urgent care (UC) visits, and only 40 percent effective at preventing hospitalizations.
Researchers analyzed acute respiratory illness-associated ED and UC visits or hospitalizations at 55 hospitals and 107 ED or UC sites within the VISION vaccine effectiveness network—a multistate collaboration with the CDC. Children and adolescents 6 months to 17 years were tested for influenza between October 2022 and March 2023.
Researchers estimated influenza A vaccine effectiveness using a test-negative design—a popular method for determining vaccine efficacy that uses the same clinical case definition for both cases and controls and distinguishes which patients are in each group with subsequent laboratory testing. In other words, the effectiveness of the influenza vaccine was estimated by comparing influenza vaccination status in patients testing positive for influenza with those testing negative for influenza.
According to the study, 13,547 of 44,787 qualified ED/UC visits and 263 of 1,862 hospitalizations were positive for influenza A. Among ED/UC patients, 15.2 percent of influenza-positive cases and 27.1 percent of influenza-negative cases were vaccinated.
The vaccine was 44 to 52 percent effective—or 48 percent effective “overall,” 47 to 58 percent effective among children aged 6 months to 4 years, and 30 to 45 percent effective among those aged 9 to 17 years old.
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