This ecological study aimed to evaluate the effect of annual revaccination
against influenza in elderly persons on trends of mortality rates and hospitalization
rates for respiratory diseases from 1990 to 2006 for mortality and from 1992 to 2006
for hospitalizations. Mortality rates for respiratory diseases increased during the
period studied. However, when it analyzed separately this trend of mortality from
pneumonia and influenza, there was decreased of mortality rates by 1996 to reverse
trend with acceleration. About hospitalization rates, it was found to decrease after
vaccine intervention, except the group above 80 years of age. Evaluating only
hospitalizations for pneumonia and influenza, hospitalization rates were increased
during the period and more pronounced in males and those older than 80 years. The
analysis of the monthly rates showed seasonal behavior with a small-scale peak
between months March to May and constant pattern in rest of the year. Among the
hypotheses to explain these findings are inequalities in vaccination coverage into
elderly population, vaccination campaign in period not optimum of the year, low
correlation between vaccine strains and predominant circulating strains of influenza
virus and circulation other pathogens related to flu-like syndromes.
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