[Seroprevalence of antibodies against measles, rubella, mumps and varicella among school children in Madrid].

OBJECTIVE: The aim of this study was to assess the seroprevalence of antibodies against MMR and varicella in a population of children between 6 and 7 years of age vaccinated against measles, mumps and rubella at 15 months of age.

PATIENTS AND METHODS: This cross-sectional study was carried out in a group of healthy children (6-7 years of age) of the Autonomous Community of Madrid, Spain. Vaccination against MMR at 15 months of age was documented for all children included in the study. Blood samples were drawn from all participants and sera were stored at -20C until they were tested at the end of the study. Measles, mumps, rubella and varicella antibody levels were measured by means of the enzyme linked immunosorbent assay (ELISA) method (IgG Genzyme Virotech GmbH). Positive values were defined as optical density values of > or = 0.20 for measles, > or = 0.30 for mumps, > or = 0.40 for rubella and > or = 0.36 for varicella. Prevalence (and the corresponding 95% confidence limits) assessed by the presence of anti-measles, anti-mumps, anti-rubella and anti-VZV antibodies on the study population were calculated. The Chi-squared test was used to evaluate differences in prevalence between sexes. The Chi-squared test was used to evaluate differences in prevalence between the sexes.

RESULTS: A total of 174 children were recruited between October and November 1997. The mean age (SD) and male/female ratio were 6.4 (0.5) years and 0.8 (45.6%/54.5%), respectively. Prevalence of antibodies against measles, rubella, mumps and varicella were 92% (88-96%), 95% (92-98%), 81% (76-86%) and 85% (90-90%), respectively. There were no significant differences between the sexes in relationship to the prevalence of measles, mumps, rubella or varicella antibodies.

CONCLUSIONS: Approximately 20% of these 6 to 7 year old children vaccinated at 15 months of age were unprotected against the mumps. Eight percent and 5% were sero-negative for measles and rubella, respectively. Administration of the second dose of MMR vaccine at 4 to 6 years of age instead of at 11 years would contribute to avoid the accumulation of non-immune children. Eighty-five percent of the study population was sero-positive for VZV. These data suggest that, in Spain, VZV infections commonly affect children younger than 5 years of age.