Effectiveness of influenza vaccination and its impact on health inequalities.

BACKGROUND Since 1998, annual publicly funded campaigns for mass vaccination against influenza of the population aged 65 years or older have been performed in the city of São Paulo, Brazil. The effectiveness of the intervention was not assessed for its contribution to the reduction of influenza-attributable mortality. This study sought to compare the age-specific mortality (65 years or older) before and after the onset of yearly vaccination, and to assess the impact of the intervention on health inequalities in relation to inner-city areas. METHODS Official information on deaths and population allowed assessment of overall pneumonia and influenza mortality. Monitoring of outbreaks and the estimation of mortality attributable to influenza peaks used Serfling and ARIMA models. Rates were compared between 1998 and 2002, when vaccination coverage ranked higher than 60% among individuals aged 65 years or older, and 1993-97 (prior to vaccination). RESULTS Overall mortality due to pneumonia and influenza fell by 26.3% after vaccination. An even higher reduction was observed for mortality specifically attributable to influenza epidemics; the number of peaks of influenza mortality also decreased. Deprived areas of the city had a higher decrease of mortality by pneumonia and influenza during the vaccination period. CONCLUSIONS Influenza vaccination contributed to reduce influenza-attributable mortality in this age group, and was associated with the reduction of inequalities in the burden of the disease among social groups. The concurrent promotion of health and social justice is feasible when there is political will and commitment to implement public health interventions with prompt and effective universal access.