[Phases 3 and 4 immunization immunogenicity with combined measles-rubella vaccine]

A two-phase combined measles-rubella vaccine (MR) immunization schedule was introduced for age 1 and prior to primary school entry in Japan in April 2006. Further immunization was also introduced for 13 (Phase 3) and 18-year-old (Phase 4) cohorts for the 5-year period from April 2008 to March 2013. We surveyed Phases 3 and 4 MR immunization immunogenicity and safety. From August 2007 to December 2009, we conducted 3 Phase 3 and 15 Phase 4 immunizations. We then took paired serum samples (pre- and 4-6 weeks post-immunization), and measured measles antibody titers using hemagglutination inhibition (HI) and neutralizing test (NT), and rubella antibody titers using HI. Pre-positive measles HI antibody titer (> or = 8) was 72% (13/18) and pre-positive measles NT antibody titer (> or = 2) was 100% (18/18). Post-positive measles HI and NT antibody titers were 94% (17/18) and 100% (18/18). Mean post-immunization measles HI and NT antibody titers were significantly higher than pre-titers, with four-fold or greater increases seen in 9 (50%) and 6 (33%) subjects. Pre-positive rubella HI antibody titer (> or = 8) was 94% (17/18), and post-positive rubella HI antibody titer 100% (18/18). Mean post-immunization rubella HI antibody titer was significantly higher than pre-titer, with four-fold or greater increases seen in 8 subjects (44%). Paired HI antibody titers were measured in pre- and post-Phase 1 immunization for measles in 3 subjects and for rubella in 2 subjects. Those with post-Phase 1 measles HI antibody titers of 32, 64, and 128 yielded titers of 16, 8, and < 8 pre-Phase 3 or Phase 4 immunization, showing antibody reduction or seronegative conversion. Those with post-Phase 1 rubella HI antibody titers of 128 and 256 yielded titers of 64 and 32 in pre-Phase 4 immunization, showing antibody reduction. Seroconversion or four-fold or greater increases in titer were seen post-immunization in 60% (3/5) of these subjects. A clinical reaction survey of all subjects 4 weeks post-immunization, showed only 1 case of mild fever and no local or systemic adverse reactions such as generalized urticaria or anaphylaxis. In conclusion, Phases 3 and 4 MR immunogenicity was satisfactory.