A ten-year follow-up study on measles vaccination in Japan: evaluation of the efficacy analyzed on a computer system

A long-term surveillance system using a computer system was established for the follow-up study on the protective effect of measles vaccination. More than 3,000 children, 3 to 6 years of age, who were immunized with measles vaccines by various methods have been registered in the system since 1971, and their outcomes with regard to measles have been followed up every year. The subjects were divided into three 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). From comparative studies with these groups, the following results were obtained: (1) Annual measles incidence rates were found to be the lowest in L group followed by FL and KL. (2) Accumulated incidence rates of measles for 10 years in L, FL and KL groups calculated were 1.90, 2.49 and 17.84%, respectively. A linear regression was observed only from 0 to 3 years after vaccination in L and FL groups, and from 0 to 9 years in KL group. KL group showed a significantly larger regression coefficient than did the former two groups. (3) Protection rates against close contact with measles in families calculated were 97% in L and FL and 80% in KL group, respectively. (4) Low but detectable levels of antibody titers were observed in the sera for at least 4--6 years after vaccination.