[Measles seroprevalence in the schoolchildren of Valencia. The Measles Study Group]

Background: People born between 1978 and 1982 were the most affected by measles in the outbreaks occurring in the Valencian Community (Spain) in 1993. This age group has not been systematically immunized against measles and has not suffered the last large measles epidemics.
Hypothesis: global seroprevalence against measles in this age group is inadequate to prevent new outbreaks.
Methods: Prospective seroepidemiologic study in a sample of school-attending children, born between 1978 and 1982. Randomized sampling of all classrooms 5th to 8th grade high school of a Health Area; stratification depending on the population of the village (< 5,000, 5,001-20,000, > 20,000 inhabitants). Antecedents of measles immunization and the disease were collected. Measles IgG antibodies were measured by enzyme immunoassay, antibody titers 1:80 or higher were considered protective.
Results: Sample of 410 subjects, belonging to 17 classes. Measles antibody prevalence was 80.2% (95% CI: 76.6-83.8%), and was higher in less populated villages (p < 0.03). Immunization status was known in 253 subjects (61.7%). Protective titers were present in 86.1% of the vaccinated and in 68.1% of the non vaccinated (p < 0.001).
Conclusions: There is a large percentage of subjects born between 1978 and 1982 unprotected against measles. Elimination of the disease will not be able unless an extraordinary vaccination campaign to include these subjects is taken.