Serological and epidemiological effects and influence factors of primary immunization with current live attenuated measles vaccine (Hu191) among infants aged 6-15 months.

A study of the serological and epidemiological effects of primary immunization with current live attenuated measles vaccine (Hu191) among 503 children aged 6-15 months, was conducted in Jingzhou, Hubei province, China from 1991 to 1998. The results showed that the positive conversion rate of measles IgG was 91.65%, geometric mean titer (GMT) was 1:266.74 and its ratio reaching protective titer was 46.52% at 1 month after first immunization. As time goes on, the above-mentioned indexes reduced rapidly. Short-term and long-term efficacy of 0.2, 0.3 and 0.5 ml measles vaccine was similar. The positive conversion rate, GMT and ratio of protective titer of IgG of different potency measles vaccine were not significantly different, however, latter two indexes showed a tendency to increase gradually with the rise of vaccine potency. The age for primary immunization was a main factor influencing immune response to measles vaccine. Immune efficacy of 6 months old group by primary vaccination was significantly lower than those of > or = 8 months old group. The result indicated it is practicable that infant aged 8 months be vaccinated with measles vaccine in China. Twenty-nine suspected measles cases were reported, out of them, 26 cases were negated in time from December 1991 to November 1998. The study showed that the short-term positive conversion rate of the enzyme immune assay IgG antibody of the Hu191 is higher, but its serological endurance isn't ideal, and its epidemiological effect should be evaluated further.