Protecting the health of the older population by vaccinating school children against influenza: A state-level analysis

Recent research suggests that children may play an integral role in the transmission of influenza to other children and other members of the community. The elderly experience particularly adverse consequences as a result of influenza. We hypothesize that, in the absence of universal vaccination, vaccinating children would have the most beneficial effect on reducing the level of pneumonia and influenza-related (P&I) hospitalizations in the elderly population (>=65). We also hypothesize that certain area-level sociodemographic factors related to social interactions on the population level, such as the proportion of children, may also affect elderly P&I outcomes. Using approximately 6.2 million hospitalization records from Medicare from 1998 to 2002, we estimated annual P&I hospitalization rates by single year of age and influenza season (July-June) by state. We obtained state-level influenza vaccination coverage in children and the elderly, plus relevant demographic characteristics from the National Immunization Survey and the US Census Bureau. It was found that P&I hospitalization rates in the elderly decreased, on average, by 3.9% (95%CI: 0.3-7.4%) for each percentage point increase in child vaccination coverage, but with no association with elderly vaccination coverage. The P&I hospitalization rates in the elderly also increased, on average, by 44% (95%CI: 7-94%) for each percentage point increase in the proportion of the population under age 5 or 85 and over. These results suggest an effective strategy to control influenza-related hospitalizations in the elderly may be to vaccinate children against influenza, particularly in states with higher proportions of both children and elderly.