Predicting the Public Health Impact of Different Adult Pneumococcal Vaccines in Japan Using a Dynamic Transmission Model

OBJECTIVES: Pneumococcal conjugate vaccines (PCVs) were introduced into a pediatric national immunization program (NIP) in Japan in 2013 and a pneumococcal polysaccharide vaccine (PPSV23) was introduced to the adult NIP in 2014. Despite an adult NIP and indirect protection from pediatric PCVs, there remains a high pneumococcal disease burden in adults.

METHODS: We calibrated a compartmental dynamic transmission model to Japan IPD data from 2008-2019. The model described Streptococcus pneumoniae carriage transmission dynamics and disease progression in the presence of age- and serotype (ST)-specific pneumococcal vaccines, capturing observed herd immunity effects and ST replacement. We used the model to evaluate three adult vaccines in 65+ year-olds: continuing the current NIP (PPSV23), introducing the recently licensed-in-adults PCV20, or introducing the new adult-focused 21-valent PCV, V116. For vaccine efficacy (VE) of adult PCVs, we assumed equivalency for vaccine type STs.

RESULTS: The model fit historical epidemiological trends across age groups and STs. At the end of the calibration, IPD incidence in 65+ year-olds was 5.39 IPD cases per 100,000, with 63% of ST-specific incidence covered by the current NIP PPSV23, 66% covered by PCV20, and 85% covered by V116. After 10 years of vaccination in the 65+ year-old population, PPSV23, PCV20, and V116 reduced IPD incidence by 0.04, 0.09, and 0.2 cases per 100,000, respectively. For STs included in V116 but not PCV20, V116 led to a decline in incidence from direct protection, while PPSV23 and PCV20 led to increases in incidence. However, for STs included in PCV20 but not V116, declines were predicted with all three adult vaccines due to herd immunity from pediatric vaccination plus direct protection in PPSV23 and PCV20.

CONCLUSIONS: The model predicted that V116 in 65+ year-olds led to greater reductions in IPD than PPSV23 and PCV20, underscoring that V116 offers greater protection against IPD to older adults than other vaccines.