MEASLES ANTIBODY-LEVELS IN A VACCINATED POPULATION IN BRAZIL

An epidemiological study of measles-specific immunoglobulin G antibody levels was conducted using a representative sample of a vaccinated su burban population in Sao Paulo State, Brazil. The study aimed to deter mine immunity status in relation to age and infection or vaccination e xperience. 549 age-structured samples of sera, collected in 1990, were screened and calibrated to the international reference serum, using m easles nucleoprotein in an enzyme immunoassay. In the age group with d irect experience of vaccination (9 months to 15 years), whether routin e or campaign, over 90% had detectable antibody greater than or equal to 50 miu/mL. However, 14% of these had antibody concentrations betwee n 50 and 100 miu/mL and 30% between 50 and 255 miu/mL. In those over 1 5 years of age, 94% had antibody levels >255 miu/mL, assumed to be the result of past infection. The study suggested that, within highly vac cinated populations, a proportion of individuals had measles antibody levels which may be insufficient to protect against reinfection or cli nical disease. The implications of these results, and similar findings elsewhere, in relation to the persistence of measles requires investi gation; this has particular relevance in Sao Paulo following the recen t measles outbreak.