Simonsen and colleagues1 question the effectiveness of influenza vaccination in the elderly because their ecologic analysis found that increases in national influenza vaccine coverage among the elderly beginning in the late 1980s were not associated with decreases in influenza-related death rate estimates. Meta-analyses of studies with data on individual vaccine status have estimated that vaccination is from 27% to 50% effective in reducing influenza-associated deaths.2,3 Estimates from meta-analyses are limited by potential selection biases in the observational studies they are based on. Yet conclusions based only on ecologic data are even less robust because no individual-level data are available concerning vaccination status or probable confounders such as the underlying health status of individuals.4,5
Thompson WW, Shay DK, Weintraub E, Brammer L, Cox NJ, Fukuda K. Influenza Vaccination Among the Elderly in the United States. Arch Intern Med. 2005;165(17):2038–2039. doi:10.1001/archinte.165.17.2038-b
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