The effect of dose and strain of live attenuated measles vaccines on serological responses in young infants.

High morbidity and mortality from measles among infants under 9 months of age is an obstacle to measles control in many developing countries. In this paper, we review 30 studies conducted on the serological response to measles vaccine in infants aged less than 9 months. Among children aged under 9 months, Edmonston Zagreb and AIK-C vaccines produce higher seroresponse rates than Schwarz vaccine of equivalent titre. For Edmonston Zagreb and Schwarz vaccine, seroresponse rates increase with increasing vaccine titre. The absolute rate of seroresponse to Edmonston Zagreb vaccine in 6-month old infants varied greatly between studies because of differences in methods of vaccine titer measurement, serological assays, definitions of seroresponse, and maternal antibody profiles of the populations studied. Seroconversion rates to Edmonston Zagreb or AIK-C vaccines at 6 months of age were generally similar to those to Schwarz vaccine at 9 months of age, but antibody levels were lower after vaccination below 9 months of age. Although the increased mortality documented in other studies after use of high titer vaccines in 4-6 month old infants led to withdrawal of these vaccines, this review of vaccine trials highlights the need for standardization of study methods and for a better understanding of the biological action of measles vaccines.