Impact of influenza vaccination of schoolchildren on medical outcomes among all residents of Maryland.

Special influenza vaccination programs of elementary school-aged children (ESAC) in some or all of Maryland Counties were conducted during the falls of 2005-2007. Rates of emergency department (E.D.) visits and hospitalizations for medically attended acute respiratory illnesses (MAARI) as well as deaths due to pneumonia and influenza for county residents were determined. The degree to which these rates were modulated during intense influenza outbreak periods (IIOP) in counties who vaccinated a greater percentage of ESAC was estimated using Poisson regression. Notably, for every 20% increase in vaccination rates, MAARI related E.D. visits during IIOP decreased by 8% (95% C.I., 5-12%) in children aged 5-11 years and by 6% (95% C.I., 3-8%) in adults aged 19-49 years (p<0.001), which suggests both a direct and indirect benefit of the vaccination programs. In contrast, MAARI related hospitalizations increased during IIOP by 4% (95% C.I., 3-9%) in adults aged >50 years for every 20% increase in vaccination rates (p<0.023) for which we have no plausible biologic explanation. No significant changes in deaths were noted.