Measles antibody titers in early infancy

To determine the prevalence of measles seronegativity among infants younger than 6 months and to ascertain their serologic response to measles vaccine.

Cross-sectional measles antibody survey during the 1989 measles epidemic in Chicago, Ill.

Inner-city perinatal center.

Two hundred three infants younger than 6 months who had been admitted to the neonatal intensive care unit at birth; 130 (64%) of these infants were premature. Transplacental antibody transfer was evaluated in a subset of 89 mother-newborn pairs.

Administration of measles monovalent vaccine to seronegative infants.

Measles IgG antibody was measured using indirect fluorescent assay. At birth, 19 (38%) of 50 neonates born at less than 37 weeks' gestation had antibody titers that were twofold 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 the 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 or more packed red blood cell transfusions (P < .001), and maternal age at delivery (P = .001). Multiple logistic regression analysis confirmed the association of seronegativity with chronological age (P < .001), gestational age (P < .02) and maternal age at delivery (P < .001). Seroconversion following administration of the measles vaccine was documented in 11 (79%) of 14 infants.

A significant proportion of 4- to 5-month-old infants who had been admitted to the neonatal intensive care unit at birth lack measurable measles antibody; this population should be taken into account when strategies to control measles are considered.