[Clinical effectiveness of antimeasles vaccine in Canarias. A case-control study]

During 1988 an outbreak of measles occurred in Gran Canaria Island. Since a certain number of cases occurred in vaccinated children, a case control study of the efficacy of measles vaccine was carried out. Fourty six cases of children aged from 15 months to 7 years were studied together with 46 age, sex, and neighbourhood matched controls. The studied cases were children who came to the Pediatric Emergency Room of the Hospital Materno-Infantil, Las Palmas, and were diagnosed of measles from the 23rd February 1988 to the 30th June 1988. The control group was formed by the first child that came to this Emergency Room right after each of the children of the measles group presenting traumatological or surgical pathology and that could be properly matched. Both measles and control children were included in the study without information about their vaccination status. In this population, the clinical efficacy of measles vaccine, corrected in order to calculate that corresponding to a cohort study given the similarity of excess reasons in the matched and not matched 2 by 2 tables, was 76.0% (confidence interval 95%: 30.4% to 85.4%). The clinical efficacy calculated by us is somewhat inferior to the 90% usually reported in the literature, nevertheless, the vaccine still has a clear, statistically significant protective effect. We believe that this diminished efficacy could be due, amongst other reasons, to a break in the cooling system or to a smaller seroconversion index in our subtropical climate. We suggest this latter aspect should be studied in detail.