The association between influenza immunization coverage rates and hospitalization for community-acquired pneumonia in Alberta

BACKGROUND: We compared regional coverage rates of influenza vaccination (composition in 1999/00 was A/Sydney-like A/Beijing-like B/Yamanashi-like and in 2000/01 was A/Moscow A/New Caledonia B/Beijing) to the rates, cost, and mortality for community-acquired pneumonia. METHODS: We used the Pearson's correlation coefficient to establish linear associations between variables derived from Alberta administrative data during the period April 1, 1999 to March 31, 2001. RESULTS: The influenza vaccination coverage rate for the 17 health regions varied between 30% to 80% (mean 70%) in Alberta seniors (n=298,473). The annual hospitalization and ambulatory community-acquired pneumonia attack rates were 2% and 6.5% per year respectively. There were strongly negative correlations between vaccination coverage rates and pneumonia rates requiring hospitalization (r1999=-0.59 and r2000=-0.79 with both p<0.05), total per capita physician and hospital costs for pneumonia (r1999=-0.57 and r2000=-0.79 with both p<0.01), community-diagnosed pneumonia rate (r1999=-0.39, p=0.12 and r2000=-0.70, p<0.01) and per capita in-hospital mortality for pneumonia (r1999=-0.30, p=0.24 and r2000=-0.57, p<0.05). Per capita costs, rates, and mortality were highest and influenza vaccinations rate lowest in the northern, remote health regions. The per capita vaccination cost (about 10 dollars) was small in relationship to the per capita cost of hospital care for pneumonia (about 100 dollars). CONCLUSION: Regional under-utilization of preventive influenza vaccination in Alberta seniors is associated with increased utilization of health services for community-acquired pneumonia.