In an intriguing study published in the ARCHIVES, Simonsen and colleagues1 conclude that observational studies have substantially overestimated influenza vaccination benefit in people 65 years and older. After adjusting for an aging US population and the frequency of influenza seasons in which the apparently more virulent influenza A(H3N2) subtype was dominant, they found that fewer than 10% of all winter deaths among people 65 years and older were attributable to influenza. That was not consistent with the meta-analysis estimate of vaccine effectiveness for all-cause mortality of 50% (45%-56%),2 which clearly suggests a much higher contribution of influenza as a cause of mortality.
Kelly H, Vu T, Smith D. Influenza Vaccination and Mortality in the United States. Arch Intern Med. 2005;165(17):2037–2038. doi:10.1001/archinte.165.17.2037-b
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