Effect of vaccine program on IgG antibody titers for measles, rubella, varicella, and mumps in young adults in Japan: Survey between 2018 and 2021

Introduction: Improved routine immunizations in Japan have led to a reduction in vaccine-preventable diseases. Due to changes in the vaccination program, current young adults received their second vaccination for measles and rubella at different times depending on their birth year, and most of them have not been vaccinated against varicella and mumps. This study investigated the effect of vaccine programs on the immunity of people in Japan. Methods: Immunoglobulin G antibody (IgG) titers against four viruses were determined by enzyme immunoassay in 795 students at a medical university. Titers for measles and rubella were compared according to the students' birth dates (Group 1: April 2, 1990-April 1, 2000; Group 2: April 2, 2000). Results: The titers of students that satisfied the standard IgG values against measles, rubella, varicella, and mumps were 24.3%, 56.9%, 87.4%, and 47.2%, respectively. Measles and rubella titers were lower in group 2 (estimated mean period from last vaccination, 7.0 years) than group 1 (13.5 years) (p = 0.023 measles, p = 0.037 rubella), indicating attenuation of titers over time. Varicella and mumps antibody prevalence indicated that these infections were endemic, whereas rates of negative titers were higher than those for measles and rubella. Conclusions: IgG titers against viruses were affected by vaccination programs. Declining titers after vaccination should be monitored when the diseases are almost eliminated and boosting is absent. Antibody testing is meaningful for recommending vaccinations and for surveillance of waning immunity. Continuous improvements of vaccination program should be considered to prevent and eliminate diseases.