MATERNAL MEASLES ANTIBODY DECAY IN RURAL BANGLADESHI INFANTS - IMPLICATIONS FOR VACCINATION SCHEDULES

Considerable numbers of measles cases occur below the target age for v accination in the Indian sub-continent. The immunogenicity of measles vaccine in infancy is dependent on the rate of decay in maternal antib ody since this antibody interferes with vaccine induced seroconversion . This study investigated maternal antibody decay in a rural populatio n in Bangladesh and evaluated possible risk factors for early decay. M easles antibodies were assessed using both ELISA and Plaque Reduction Neutralization (PRN) test in 330 infant-mother pairs in a cross-sectio nal survey. PRN was more sensitive method than ELISA for determining a ntibody levels. Antibody levels decreased rapidly in infants with incr easing age. By the age of 5 months, 67% (28/42) infants had practicall y no protective antibody left (30 mIU ml(-1) or below). Only 12% infan ts at 5 months of age, and 5% at 8 months, had levels greater than 120 mIU ml(-1)-stated to 'protect' children. Multiple regression showed t hat maternal age was the only variable associated with the level of an tibody (maternal weight, height and MUAC were not associated), decreas ing by 1.06 mIU ml(-1) for each year of age (P = 0.002). Infant's anti body concentration decreased with age by an average 2 mIU ml(-1) for e very month of life (P < 0.0001), and was determined by the maternal an tibody concentration (P < 0.0001) (child's length, weight, MUAC, mothe r's gestational age and parity were not associated). The relatively ra pid antibody decay suggests that the target age for measles vaccinatio n might be reduced. Further, as the cohort of vaccinated mothers enter s reproductive age in Bangladesh, a more rapid decay of antibody may b e expected in future generations of Bangladeshi children. The informat ion presented here suggests that a formal trial of standard measles va ccine at younger ages is justified in this population as it could conf er considerable benefit in reducing infant measles. (C) 1998 Elsevier Science Ltd. All rights reserved.