Measles vaccine immunogenicity and antibody persistence in 12 vs 15-month old infants

Hypothesis: Maternal measles immunity in the United States today is primari ly vaccine induced, with corresponding lower antibody titers in infants, as compared to infants born in an earlier era to mothers with naturally acqui red measles immunity. We hypothesized that, due to lower titer of passively transferred maternal measles antibody, administration of measles vaccine a t 12 months of age would result in seroconversion and antibody persistence comparable to vaccination at 15 months of age. Population: Children at both an urban hospital and a suburban clinic. Methods: Informed consent was obtained from mothers for the infants to rece ive M-M-R(R)II vaccine at either 12 or 15 months and to have serum samples obtained before vaccination and 4 weeks post-vaccination (PV). Between 9 an d 39 months PV, a third serum sample was obtained from 28% of seroconverter s. A diary of adverse experiences was kept for 3 weeks PV. Sera were assaye d by a microneutralization assay (NT) and an enzyme immunoassay (EIA) for m easles antibody. Results: Both age groups tolerated vaccination well with minor and transien t side effects. Forty-four of 47 (94%) 12-month-old infants seroconverted b y NT, compared to 45 of 46 (98%) 15-month-olds (p = NS). There was no stati stically significant decline in median NT titers or EIA titers in nineteen 12-month-olds and thirteen 15-month olds followed for 9-39 months PV. Conclusion: This study showed comparable serologic responses in 12- vs 15-m onth-old infants born to measles vaccine-immune mothers; however, the sampl e size was too small to have adequate power and further study is indicated, Titers of antibody were constant in both the 12-month-old and the 15-month -old infants, over a 9-39 month period, suggesting that waning immunity ove r this period of time is not a problem in either age group. (C) 2000 Elsevi er Science Ltd. All rights reserved.