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Results of the evaluation of the anti-meningococcal BC Cuban vaccine based on routine epidemiological surveillance information of meningitis for the years 1990 to 1992, following mass-vaccination of 232,022 children aged between 3 months and 7 years in 1989/90 during an epidemic of serogroup B meningococcal disease in the State of Santa Catarina, Brazil, are presented. The protective efficacy of the vaccine was calculated from the incidence rates for the cohort of vaccinated and non-vaccinated children in 20 municipalities. Main results for cases confirmed by bacteriological tests were 59% (CI 95%: 23 to 78%) for children aged under 4 years and 78% (CI 95%: 54 to 90%) for children aged 4 to 7 years. Eighty-six percent of cases serogrouped (n = 29) were B, and in these cases efficacy increased to 66% (< 4 years) and 88% (4-7 years), but at 95% CI were wider. The protective efficacy based on death rates from the disease in children < 4 years was 76% (CI 95%: 41 to 91%). There was no evidence of decreasing protective efficacy in the three year follow-up, as shown by the yearly estimates. An interesting hypothesis arising from the findings is that the lower protective efficacy for children aged < 4 years, observed in studies in which only cases confirmed by laboratory tests are analysed, could be due to a selective effect of this procedure. More severe cases die shortly after the onset of the disease, often before medical care is provided. On the other hand, the attenuation of the disease by vaccination gives a better chance for medical intervention and collection of samples for laboratory analysis. Finally, the authors support the use of the vaccine in epidemics of serogroup B meningococcal disease. They also suggest that three, rather than two doses of vaccine should be tested in children under 2 years of age to further increase its efficacy.