Application of the screening and indirect cohort methods to evaluate the effectiveness of pneumococcal vaccination program in adults 75 years and older in Taiwan

BACKGROUND: The Taiwanese national 23-valent pneumococcal polysaccharide vaccine (PPV23) program in adults ≥75 years of age and the 13-valent pneumococcal conjugate vaccine (PCV13) program for children were implemented in 2008 and 2013, respectively. In this study we evaluated PPV23 vaccine effectiveness (PPV23VE) in the elderly, with regard to both direct protection from the vaccine itself and the indirect protection conferred by PCV13 immunization in children. METHODS: The incidence of invasive pneumococcal disease (IPD) in Taiwan from July 2008 to June 2016 was collected from IPD surveillance data. A comparison of IPD incidence with a nationwide vaccination registry allowed an estimation of PPV23VE by the screening and indirect cohort methods. RESULTS: The incidence of IPD in adults ≥75 years of age ranged from 13.9 per 100,000 inhabitants during the period July 2008–June 2013 to 10.4 per 100,000 inhabitants between July 2013 and June 2016 (relative risk [RR]: 0.75; 95% confidence interval [95% CI]: 0.67–0.85). According to the screening method, PPV23VE against death within 30 days of IPD onset, all IPD, and PPV23-serotype IPD was 32.5% (95% CI: 17.5–44.7%), 33.9% (95% CI: 25.2–41.5%) and 43.4% (95% CI: 34.4–51.2%), respectively. PPV23VE with the indirect cohort method was 39.0% (95% CI: 15.5–55.9%) for all PPV23 serotypes and 71.5% (95% CI: 44.2–85.4%) for 11 serotypes included in PPV23 but not in PCV13. During the period July 2008–June 2012, PPV23VE against PPV23-serotype IPD was 55.1% (95% CI: 27.2–72.3%). CONCLUSIONS: PPV23 is able to prevent IPD and 30-day fatality in adults 75 years of age and older due to a combination of direct effects from PPV23 and indirect effects from PCV13. It might confer higher protection against PPV23-serotype IPD before the introduction of PCV13 program in children. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12879-020-05721-0.