Trends in varicella and mumps vaccination rates in children under 3 years of age in a tertiary children's hospital in Japan.

Background: In Japan, the voluntary vaccination rate is not known accurately. Although two doses of the measles and rubella vaccines have been part of the universal vaccine program since 2006, the varicella vaccine was added in October 2014 while the mumps vaccine still remains voluntary. The aim of this study was to evaluate trends in the live measles, rubella, varicella and mumps vaccination rates in Japan.

Methods: This retrospective cohort study was conducted at Tokyo Metropolitan Children's Medical Center between October 2012 and December 2016. Patients aged 1-2 years who were admitted to the Department of General Pediatrics were enrolled. The trend in the vaccination rate against measles, rubella, varicella, and mumps was examined.

Results: The measles and rubella vaccination rate was 80-90%. The varicella vaccination rate in the second quarter of 2012, the third quarter of 2014, and the fourth quarter of 2016 was 34.6%, 67.1%, and 80.7%, respectively. The mumps vaccination rate in the second quarter of 2012, the third quarter of 2014, and the fourth quarter of 2016 was 27.6%, 59.5%, and 61.8%, respectively.

Conclusions: The varicella and mumps vaccination rate improved until 2014 despite the fact that they were voluntary vaccinations. After varicella vaccination was added to the universal vaccination program, the varicella vaccination rate continued to improve. The mumps vaccination, which was not included, failed to improve, suggesting that the universal vaccination program contributed to increasing the uptake of the vaccines it includes.