Impact and vaccine effectiveness of the 23-valent pneumococcal polysaccharide vaccine in adults aged 65 years or older in the Netherlands

Objectives The 23-valent pneumococcal polysaccharide vaccine (PPV23) was introduced into the Dutch national immunisation programme in 2020 to reduce invasive pneumococcal disease (IPD) and pneumococcal pneumonia among older adults. We evaluated the impact and vaccine effectiveness of PPV23 against vaccine-type IPD during the first 3 years after implementation, covering individuals born between 1941–1947 (70–73 years old in 2020), 1948–1952 (69–73 years old in 2021), and 1953–1956 (65–69 years old in 2022). Methods Impact and vaccine effectiveness (VE) were estimated using national surveillance data for IPD from the three season-years postimplementation (2020/21–2022/23). Vaccination programme impact, expressed as relative reduction of the vaccine-type IPD incidence in eligible age groups, was assessed using a regression discontinuity analysis, exploiting age-based vaccine eligibility. VE against vaccine-type IPD was estimated, stratified by year and birth cohort, with a complier average causal effect analysis. Results Regression discontinuity analysis showed a significant reduction in vaccine-type IPD incidence among vaccine-eligible adults, with estimated impacts of 43.9% (95% credible interval [CrI], 24.2; 60.9), 34.8% (95% CrI, 16.5; 50.6) and 32.1% (95% CrI 14.8; 46.9) for the 2020–2021, 2021–2022, and 2022–2023 seasons, respectively. Complier average causal effect analysis indicated statistically significant VE for all eligible cohorts, ranging from 48.1% to 73.1% (95% CrI ranging, 20.7–83.6). Conclusions The Dutch PPV23 immunisation programme led to a consistent and substantial reduction in vaccine-type IPD among older adults. Additionally, PPV23 vaccination provided a statistically significant protective effect against vaccine-type IPD among vaccinated individuals during the first 3 years after vaccination.