MEASLES ANTIBODY-TITERS IN EARLY INFANCY

Objective: To determine the prevalence of measles seronegativity among infants younger than 6 months and to ascertain their serologic respon se to measles vaccine. Design: Cross-sectional measles antibody survey during the 1989 measles epidemic in Chicago, Ill. Setting: Inner-city perinatal center. Participants: Two hundred three infants younger tha n 6 months who had been admitted to the neonatal intensive care unit a t birth; 130 (64%) of these infants were premature. Transplacental ant ibody transfer was evaluated in a subset of 89 mother-newborn pairs. I ntervention: Administration of measles monovalent vaccine to seronegat ive infants. Measurements/Results: Measles IgG antibody was measured u sing indirect fluorescent assay. At birth, 19 (38%) of 50 neonates bor n at less than 37 weeks' gestation had antibody titers that were twofo ld to fourfold lower than those of their mothers compared with three ( 8%) of 39 neonates born at more than 37 weeks' gestation (P<.01). Of t he 203 study infants, fewer than 4% were seronegative at birth, while 74% of these infants aged 4 to 5 months were seronegative. Univariate logistic regression analysis indicated that the independent variables related to seronegativity were as follows: gestational age at birth (P =.007), chronological age (P<.001), history of having received three o r more packed red blood cell transfusions (P<.001), and maternal age a t delivery (P=.001). Multiple logistic regression analysis confirmed t he association of seronegativity with chronological age (P<.001), gest ational age (P<.02), and maternal age at delivery (P<.001). Seroconver sion following administration of the measles vaccine was documented in 11 (79%) of 14 infants. Conclusion: A significant proportion of 4- to 5-month-old infants who had been admitted to the neonatal intensive c are unit at birth lack measurable measles antibody; this population sh ould be taken into account when strategies to control measles are cons idered.