COOPERATIVE MEASLES VACCINE FIELD TRIAL

Abstract

The efficacy of two measles vaccine schedules was tested in a double-blind, placebo-controlled field trial. One group of children received three injections of 0.5 ml of inactivated measles virus vaccine. A second group received two injections of inactivated measles virus vaccine followed by 1400 TCID50 of live attenuated virus measles vaccine. Half of the participating children received placebo injections. The 4,758 participating children in kindergarten and first and second grades were kept under surveillance over a period of 14 months. Among these children 504 cases of clinically diagnosed measles occurred; 430 were in the placebo group. The inactivated measles virus vaccine, although providing good protection against cases of typical severity during the immediate 3 months after vaccination, showed a progressively decreasing level of efficacy over a year's period. At the end of a year, efficacy had fallen to 75%. The combined vaccine schedules demonstrated a consistently high order of protection, of about 95% or better, throughout the study period. The efficacy of two measles vaccine schedules—three injections of 0.5 ml of inactivated measles virus vaccine and two doses of inactivated virus vaccine followed by one dose of live vaccine—was tested in a double-blind, placebo-controlled study among 4,758 children in kindergarten and first and second grades. Measles hemagglutination inhibition antibody titers were measured on a randomly selected sample of study participants immediately before and 1, 8, and 14 months after the third injection. Although over 90% of those given the inactivated virus vaccine demonstrated detectable hemagglutination inhibition antibody 1 month post-vaccination, only 50% were seropositive 14 months later. Some clinically typical measles cases did occur among children in whom the inactivated virus vaccine had evoked an initial antibody response. Of those children receiving two doses of inactivated virus vaccine followed by live vaccine, 97% showed seroconversion 1 month post-vaccination. Fourteen months later 89% still had detectable antibody. Fourfold or greater titers occurred in some children in both vaccine groups without evident clinical measles illnesses. These titer "boosts" were considered to be on the basis of subclinical measles infections.