Loss of maternal measles antibody in black South African infants in the first year of life implications for age of vaccination

In order to investigate the feasibility of measles vaccination before the age of 9 months the duration of passive immunity against measles was estimated by conducting a longitudinal study of measles antibody levels in 20 black neonates delivered at term. Measles serum antibody (lgG) was measured by enzyme-linked immunosorbent assay in the mother at childbirth and on consecutive samples taken from the infants from birth until 9 months of age. Protective measles antibody level was defined as > 200 mlU. Unprotective levels were found in 88% (95% confidence interval (Cl) 81 - 99%) of 6-month-old infants, while at 9 months all were susceptible. The mean antibody level was 192 mlU (Cl 104 - 348%) at 4 months; 34 mlU (Cl 15 - 73%) at 6 months and 13 mlU (Cl 6-24%) at 9 months of age. Our data support the recent World Health Organisation recommendation to immunise children in developing countries at 6 months with the 'high titre' Edmonston-Zagreb measles vaccine, since most infants in our study had lost passive immunity against measles by this age