A TEN-YEAR FOLLOW-UP STUDY ON MEASLES VACCINATION IN JAPAN*: EVALUATION OF THE EFFICACY ANALYZED ON A COMPUTER SYSTEM

Abstract
A long-term surveillance using a computer system was established for the follow-up study on the protective effect of measles vaccination. More than 3000 children, 3-6 yr of age, who were immunized with measles vaccines by various methods were registered in the system since 1971, and their outcomes with regard to measles were followed up every year. The subjects were divided into 3 groups by the vaccination method: live vaccine alone (L), further attenuated live vaccine alone (FL) and the combined use of live and killed vaccines (KL). Annual measles incidence rates were the lowest in L group followed by FL and KL. Accumulated incidence rates of measles for 10 yr in L, FL and KL groups were 1.90, 2.49 and 17.84%, respectively. A linear regression was observed only from 0-3 yr after vaccination in L and FL groups, and from 0-9 yr in KL group. KL group showed a significantly larger regression coefficient than did the former 2 groups. Protection rates against close contact with measles in families were 97% in L and FL and 80% in KL group. Low but detectable antibody titers were observed in the sera for at least 4-6 yr after vaccination.