Mumps virus vaccine (Sinovac (Dalian) Vaccine Technology Co. Ltd.)

Continuous mumps vaccine coverage is essential for eradicating mumps. However, due to safety concerns, Japan's mumps vaccination program transitioned from routine to voluntary. To improve coverage, some municipalities introduced subsidization programs, but the effects on vaccination rates and mumps incidence remain unclear.

In April 2018, a city in Japan launched a subsidization program for the mumps vaccine for children aged 1-6 years. Using vaccination records and healthcare claims from July 2016 to December 2019, we analyzed changes in vaccination coverage and mumps incidence before and after the program's initiation.

At the program's start, mumps vaccination coverage among eligible children was 3.3%, increasing by approximately 1.5% monthly to 38.4% after 21 months. Among 308,976 individuals, 145 mumps cases were identified: 92 cases (0.27 per 1,000 person-years) occurred before, and 53 (0.15 per 1,000 person-years) occurred after the program's start.

Although the mumps vaccination coverage rate increased following the program's initiation, it remained below the level required for eradication.

Recently, live-attenuated measles, rubella, varicella, and mumps vaccines have been administered to carefully selected post-liver transplant patients. Although attention has been focused on post-vaccination antibody titers and adverse events, the real-life clinical benefits remain unclear. A comprehensive analysis of breakthrough infections and natural boosters (asymptomatic cases with significant elevation in virus antibody titers) following immunization post-liver transplantation was conducted from 2002-2023, exploring the timing, frequency, correlation with domestic outbreaks, and degree of antibody elevation. During the median 10-year observation period among 68 post-liver transplant patients, breakthrough infections occurred only in chickenpox, with 7 mild cases (1 episode/64 person-years). A total of 59 natural booster episodes (1, 5, 20, and 33 for measles, rubella, chickenpox, and mumps, respectively) were observed, with incidence rates of 1 per 569, 110, 22, and 17 person-years, respectively. The timing of natural boosters closely correlated with domestic outbreaks (P < .05 in chickenpox and mumps), influenced by local vaccine coverage. The degree of antibody elevation was significantly higher in individuals with breakthrough infections than in those with natural boosters (P < .05). These findings suggest that immunization with live-attenuated vaccines for post-liver transplant patients has demonstrated clinical benefits. Furthermore, mass vaccination has a positive impact on post-transplant patient outcomes.