Influenza-associated morbidity in Florida seniors: No association between influenza burden and influenza vaccination coverage

Recent research questions the strategy of vaccinating older adults against influenza to prevent the spread of influenza in this vulnerable population subgroup. Our past findings on the state level showed significant negative associations between influenza vaccination coverage in children and influenza rates in older adults, but no significant associations between vaccination coverage in older adults and influenza rates. The purpose of this study was to assess the association between influenza vaccination coverage and influenza burden in older adults and influenza burden by county in Florida. We abstracted approximately 800,000 influenza-associated Medicare hospitalization records to calculate three outcomes of disease burden in older adults: age-adjusted disease rates, age-specific disease rates, and age-acceleration of rate. We compared these rates with influenza vaccination coverage in older adults for the two influenza seasons, 2002-03 and 2006-07, available from the Behavioral Risk Factor Surveillance System using the generalized estimation equation to account for repeated measurements and covariates. In models that were unadjusted or adjusted for socio-demographic characteristics, there was no statistically significant association between vaccination coverage in seniors and age-adjusted disease rates (p = 0.545) or age acceleration in disease rates (p = 0.399). There was, however, a modest, but statistically significant positive association between vaccination coverage in seniors and age-specific disease rates, particularly for 65-74 year-olds (p = 0.01). Although absence of evidence does not indicate evidence of absence, these findings suggest that there may be more effective strategies to reduce influenza burden in older adults than the prevailing strategy of vaccinating seniors themselves against influenza.