CHANGING LEVELS OF MEASLES ANTIBODY-TITERS IN WOMEN AND CHILDREN IN THE UNITED-STATES - IMPACT ON RESPONSE TO VACCINATION

Objectives. In the United States, younger women are more likely to hav e immunity to measles from vaccination and are less likely to have bee n exposed to the wild virus than are older women. To evaluate changes in measles antibody titers in women in the United States and children' s responses to measles vaccination, we analyzed data from a measles va ccine trial. Methods. Sera collected from children before vaccination at 6, 9, or 12 months of age and from their mothers were assayed for m easles antibodies by plaque reduction neutralization. Responses to vac cination with Merck Sharp & Dohme live measles virus vaccines at 9 mon ths (Attenuvax) and 12 months (M-M-R II) were also analyzed. Results. Among women born in the United States (n = 614), geometric mean titers (GMTs) of measles antibodies decreased with increasing birth year. Fo r those born before 1957, 1957 through 1963, and after 1963, GMTs were 4798, 2665, and 989, respectively. Among women born outside of the Un ited States (n = 394), there were no differences in GMTs by year of bi rth. Children of younger women born in the United States were less lik ely than those of older women to be seropositive at 6, 9, or 12 months . The response to the Vaccines varied by maternal birth year for child ren of women born in the United States. Among 9-month-old children, 93 % of those whose mothers were born after 1963 responded, compared with 77% and 60% of those whose mothers were born in 1957 through 1963 and before 1957, respectively. Among 12-month-old children, 98% of those born to the youngest mothers responded, compared with 90% and 83% of t hose whose mothers were born in 1957 through 1963 and before 1957. The responses of children of women born outside of the United States were not associated with maternal year of birth. Conclusions. An increasin g proportion of children in the United States will respond to the meas les vaccine at younger ages because of lower levels of passively acqui red maternal measles antibodies.