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Annual trends in adverse events following mumps vaccination in Japan: A retrospective study
Satoko Ohfuji1, Takaaki Tanaka2, Takashi Nakano2
1Department of Public Health, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka-city, Osaka 545-8585, Japan; Research Center for Infectious Disease Sciences, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka-city, Osaka 545-8585, Japan.
Background:
In Japan, a monovalent mumps vaccine is provided on a voluntary basis. Due to public concerns over post-vaccination aseptic meningitis, the vaccination coverage is not high enough. The present study investigated the incidence of adverse events, including aseptic meningitis, after Torii strain-derived mumps vaccination.
Methods:
This retrospective, observational study used data collected by a vaccine manufacturer regarding adverse events following mumps vaccinations at medical institutions between 1992 and 2018. In addition, the number of Torii strain-derived mumps vaccines shipped each year was obtained. The incidence (per 100,000 doses) and 95% confidence intervals (CIs) were calculated for all adverse events and each adverse event, categorized as aseptic meningitis, encephalitis, mumps, mumps complications, and others.
Results:
During the study period, 8,262,121 mumps vaccine doses were shipped, and 688 subjects reported adverse events. The incidence for all adverse events (per 100,000 doses) was 8.33, and the incidence was 4.19 for aseptic meningitis, 0.33 for encephalitis, 0.80 for mumps, 0.25 for mumps complications, and 3.78 for others. The incidence of aseptic meningitis (per 100,000 doses) was 7.90 (95% CI: 5.61-10.18) between 1998 and 2000 but declined by half, to 3.91 (2.46-5.36), between 2001 and 2003. The most recent incidence (per 100,000 doses) of aseptic meningitis, for the period 2016 to 2018, was 2.78 (1.94-3.62).
Conclusion:
The incidence of post-vaccination aseptic meningitis has declined significantly since 2001, and the incidence has remained stable at fewer than 3 cases per 100,000 doses since 2010. Multiple factors might have contributed to the decline in aseptic meningitis incidence, including (i) lowered misclassification of aseptic meningitis resulting from echovirus infection; (ii) changes in the vaccine manufacturing process in 2000; and (iii) publication in 2008 of the recommendation for vaccination of children at 1 year of age.
Insights
Concerns about mumps vaccine safety, specifically aseptic meningitis, have decreased. Post-vaccination aseptic meningitis incidence has significantly declined, remaining stable at under 3 cases per 100,000 doses since 2010.
Area of Science:
- Vaccinology
- Epidemiology
- Public Health
Background:
- Monovalent mumps vaccine in Japan is voluntary.
- Low vaccination coverage is linked to concerns about post-vaccination aseptic meningitis.
- This study examines adverse events following Torii strain mumps vaccination.
Purpose of the Study:
- To investigate the incidence of adverse events, including aseptic meningitis, after Torii strain-derived mumps vaccination.
- To assess trends in adverse event incidence over time.
- To address public concerns regarding mumps vaccine safety.
Main Methods:
- Retrospective, observational study using vaccine manufacturer data (1992-2018).
- Analysis of adverse events and vaccine shipment data.
- Calculation of incidence rates and 95% confidence intervals for adverse events.
Main Results:
- Over 8.2 million mumps vaccine doses were shipped; 688 adverse events reported.
- Overall adverse event incidence: 8.33 per 100,000 doses.
- Aseptic meningitis incidence: 4.19 per 100,000 doses, declining from 7.90 (1998-2000) to 2.78 (2016-2018).
Conclusions:
- Post-vaccination aseptic meningitis incidence has significantly decreased since 2001.
- Incidence has remained stable at <3 cases per 100,000 doses since 2010.
- Declines may be due to reduced misclassification, manufacturing changes, and updated vaccination recommendations.
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