Passive acquired immunity against measles in infants born to naturally infected and vaccinated mothers.

BACKGROUND: Currently, the majority of newborns in Poland are born to mothers who have been immunized against measles. The aim of this study was to compare the maternal measles antibody titers of infants born to mothers who had been infected by measles wild virus (group I) with those born to mothers who had been vaccinated (group II). MATERIAL/METHODS: Serum samples were tested for measles antibodies from 79 infants in the 7th month of life and from 27 mothers between 17 and 41 years of age. Two commercial enzyme immunoassays (EIA) and a plaque neutralization test (PNT) were used. RESULTS: Only 12.7% of all infants showed measles antibodies in EIA. However, antibodies could be detected by PNT in all the infants, although only 36.6% showed titers of >1:8, which corresponds to protective antibody values of >0.2 IU/ml. The mean geometrical titer was significantly higher among infants from group I than in group II (1:7.16 vs. 1:3.71, p=0.0038). Protective antibody titers were detected in 50% of infants from group I and only 18.2% in group II (p<0.02). CONCLUSIONS: Passive acquired immunity in infants born to mothers who have had measles lasts longer than in infants born to vaccinated mothers. Nearly two thirds of infants (65.4%) in the 7th month of life did not have sufficient maternally derived neutralizing antibodies to protect against measles. Our data suggest that the recommended age for the first dose of measles vaccine during measles epidemics should be lowered to 9 months, with re-vaccination at 12-15 months.