CLINICAL EFFECTIVENESS OF INFLUENZA VACCINATION IN MANITOBA

Objective.-To assess the clinical effectiveness of influenza vaccinati on in preventing influenza-associated hospitalization and death. Desig n.-Case-control study. Setting and Patients.-Noninstitutionalized pers ons aged 45 years or older living in Manitoba, on December 1, 1982, an d December 1, 1985. Methods.-Linked records of the Manitoba population registry, hospital-discharge abstracts, physician claims for ambulato ry-patient visits and influenza vaccination, and vital statistics were used. A matched-set analysis estimated the clinical effectiveness of influenza vaccination in preventing hospital admissions and deaths fro m influenza-associated conditions during influenza A (H3N2) outbreak p eriods in 1982 to 1983 (12 weeks) and 1985 to 1986 (10 weeks). The ana lysis adjusted for hospital discharge and ambulatory care for high-ris k conditions within the previous 15 months and 3 months, respectively. Results.-Influenza vaccination prevented 32% to 39% of hospital admis sions with pneumonia and influenza and 15% to 34% of admissions with a ll respiratory conditions. Vaccination was 43% to 65% effective in pre venting hospital deaths with these conditions (all listed diagnoses) a nd 27% to 30% effective in preventing deaths from all causes. Conclusi on.-Influenza vaccination has substantial clinical effectiveness in pr eventing hospital admission and death from influenza-associated condit ions in noninstitutionalized individuals.