Comparison of two vaccination programmes in preventing influenza-related hospitalization among the elderly during two...

The protective effect of influenza vaccine against influenza related hospitalization is well established at an individual level, but the effect of vaccination programme at the population level is unknown. In this study we compared a risk disease-based free-of-charge influenza vaccination programme in preventing hospitalizations due to influenza or pneumonia and cardiovascular diseases during 2 consecutive influenza seasons 1992/93 and 1993/94 in 43 municipalities in northern Finland. Vaccinations were carried out and reported by local staff in health centres. Data of hospital treatment periods were obtained from the National Hospital Discharge Register. During the influenza seasons the number of hospitalizations due to cardiovascular diseases and influenza/pneumonia increased by 13%. In the 1993/1994 season the increase in the study area with the risk disease-based vaccination programme was 22 per 1000 persons (95% CI 19-24), and with an age-based programme 3.3 per 1000 persons (95% CI 2.5-4.0), while the increase in the 1992/1993 season in both areas was 3-4 per 1000. The excess of hospitalization related to influenza epidemics is mostly due to cardiovascular diseases and varies from y to y, as do the benefits gained by vaccination.