Measles antibody prevalence after mass immunization in São Paulo, Brazil

In 1987, a mass immunization campaign against measles was carried out in the greater metropolitan region of São Paulo, Brazil. During a ten-day period, 4,194,174 children from 9 months to 14 years old, representing 86% of the target population, were vaccinated regardless of their previous vaccination status. Four months later, the prevalence of measles antibodies was evaluated through a random seroepidemiological survey. The survey included all children in greater São Paulo between one month and 14 years old, irrespective of campaign participation. Blood samples were collected on filter-paper and tested for measles antibody by indirect immunofluorescence. Negative or doubtful cases were tested again using an immunoenzymatic assay (ELISA). Of the 8661 samples included in the study, 8146 (94.1%) were positive for measles antibody. In children aged one year or more a significant difference in antibody prevalence was observed when comparing those who were vaccinated during the mass immunization (98.0%) with those who did not participate in the campaign (91.3%). In addition, after the immunization, a marked and immediate decrease was observed in incidence rates for measles cases notified to the State Secretary of Health, falling from 222/100,000 inhabitants in 1987 to 2.7/100,000 in 1988. These data suggest that mass immunization can serve as an additional strategy for the rapid control of measles in developing countries.