Younger US-born mothers are more likely to have measles vaccine-induced immunity than are older mothers and are less likely to have been boosted by exposure to wild virus. To assess whether younger mothers have lower antibody titers and whether their children lose antibody at a younger age, we determined pre-vaccination plaque reduction neutralization (PRN) measles antibody titers in infants at either 6,9, or 12 months of age and their mothers who were enrolled in a measles vaccine trial in LA, CA. Sera collected from 913 mothers (n=527), those born <1957 had a higher PRN geometric mean titer (GMT) than those born >1957 (4707 vs. 1592, P<0.001). Among non-US born mothers (n=386), there were no differences in GMT by year of birth (1854 vs 2142). Children born to younger US-born mothers were more likely to be seronegative than those born to older mothers at 6 months (47% vs 17%, p=0.003), 9 months (65% vs 36%, p<0.001), and 12 months (88% vs 82%, p=NS). Response rates to Moraten measles vaccine were higher in children born to younger compared with older US-born mothers at 9 months (87% vs 58%, p=0.008) and 12 months of age (94% vs 83%, p=NS). Response rates to measles vaccine in the US may be higher in infants than previously reported due to lower levels of maternal antibody in children born to younger women.
