Serum specimens, collected in the county of Huixquilucan, State of México, México, and nationwide in Paraguay, were studied for hemagglutination-inhibition antibody to measles and rubella. The Mexican sample population comprised 667 children up to 17 years of age, and the Paraguayan sample was composed of 408 children of comparable ages. Tests revealed that preschool children in both study populations acquired antibody to measles virus fairly rapidly; 70.9% and 65.4% of the Mexican and Paraguayan children, respectively, had antibody to measles virus at the age of 7 years. In comparison to the Mexican children, however, Paraguayans of school age had a consistently higher prevalence of measles antibody; and in cohorts older than 8 years antibody prevalence ranged from 91.2% to 100%. Measlesantibody prevalence in similar cohorts in México ranged from 75% to 88.2%. Seroconversion to rubella virus among Paraguayan children studied was drastically slower than that seen among Mexican children. By the age of 7 years, only 17.1% of Paraguayans had rubella antibody in contrast to 75.8% seroconversion in México. Even more striking was the finding that there were no rubella-seronegative children among cohorts 13 years of age, or older, in Huixquilucan. Possible mechanisms for the unusually high prevalence of antibody to rubella are discussed.
Present address: Fitzsimmons General Hospital, Denver, Colorado 80240.