Influenza vaccination in young children reduces influenza-associated hospitalizations in older adults, 2002-2006.

OBJECTIVES: To assess how influenza vaccination coverage in children is related to pneumonia and influenza (P&I) in older adults and whether sociodemographic factors modify these associations.
DESIGN: Approximately 5 million hospitalization records from the Centers for Medicare and Medicaid Services for four influenza years (2002-2006) were abstracted. A single-year age distribution of rates of P&I hospitalization was estimated according to state for each influenza season; an exponential acceleration in the P&I rates with age was observed for each influenza season. State- and season-specific P&I rate accelerations were regressed against the percentage of vaccinated children, older adults, or both using mixed effects models.
SETTING: U.S. population, 2002 to 2006. PARTICIPANTS: U.S. population aged 65 and older. MEASUREMENTS: State-level influenza annual vaccination coverage data in children and older adults were obtained from the National Immunization Survey and the Behavioral Risk Factor Surveillance System, respectively.
RESULTS: Child influenza vaccination coverage was negatively associated with age acceleration in P&I, whereas influenza vaccination in the older adults themselves was not significantly associated with P&I in older adults.
CONCLUSION: Vaccination of children against influenza may induce herd immunity against influenza for older adults and has the potential to be more beneficial to older adults than the existing policy of preventing influenza by vaccinating older adults themselves.