In term infants, maternal antibody may interfere with seroconversion to measles vaccine up to one year of age. This study evaluated the persistence of maternally derived measles antibodies in premature infants and infant response to measles, mumps, rubella (MMRII) vaccination at 9 or 12 months. Serum was collected at birth, 2-4, and 7 months of age from 97 premature infants with birthweights of <1000, 1000-1499, 1500-2499 grams. Measles-specific antibodies were measured by an indirect IgG EIA and a microneutralization(mNT) assay. Table 1 shows the mNT results for each birthweight group over time; seropositivity was defined as a titer > 1:10. To date, 48 seronegative infants have been randomized to MMRII vaccination at 9 or 12 months old and serum was collected 3 months later. Of 26 infants vaccinated between 8.5 and 10.5 months old, 21/24 (88%) and 25/26 (96%) were seropositive by mNT and EIA, respectively. Of 22 infants vaccinated between 11.5 and 13.5 months old, 18/18 and 22/22 were seropositive by mNT and EIA, respectively. Premature infants are susceptible to measles earlier than term infants and may benefit from early MMRII vaccination. Persistence of antibodies at 18-24 months will be evaluated.

Table 1 Percent (# tested) Seropositive by Microneutralization over Time
Full size table