Measles passive immunity in infants from vaccinated and disease acquired mothers

Abstract

Background — Despite the decline in the incidence of measles in Chile, epidemics continue to occur. In Chile, measles vaccine is administered at one year of age, therefore, we hypothesized that control of epidemic measles may be improved with a better understanding of the immunologic status of infants. Objective — To evaluate the immunologic status to measles of unvaccinated infants born to previously vaccinated and disease exposed mothers. Method — Group A subjects were pregnant women with a documented history of measles infection, and group B subjects were pregnant women with a documented history of measles vaccination. Maternal blood samples and cord blood were obtained immediately following delivery. Blood samples were obtained from infants at 6 and 9 months of age. Samples were tested for anti-measles antibodies using an ELISA technique. Results — There were 41 subjects in group A and 35 in group B. Infant birth weight and the mothers age were comparable in the two groups. At delivery the titre of measles antibodies in cord blood was the same in the two groups. A higher mean antibody level pre-delivery was observed in group A (disease exposed) mothers compared with group B (vaccinated) (p = 0.028). There was a significantly lower antibody titre at 6 months and 9 months compared with baseline in both groups (p = < 0.001), but no difference in titre between infants born to vaccinated versus disease exposed mothers. The levels of antibody titre were below protective levels at 6 and 9 months. Conclusion — There is a rapid decline in measles antibody levels observed by 6 months in infants from mothers either previously exposed to measles or vaccinated. There is inadequate protection of infants from measles by 6 months based on immunological status, with no difference in infant immunologic status of infants from disease exposed and previously vaccinated mothers.