Effect of pneumococcal conjugate vaccine booster dose on prevention of invasive pneumococcal disease in British Columbia, 2003–2018

Background: Invasive pneumococcal disease (IPD) remains a major cause of morbidity in children despite the routine use of pneumococcal conjugate vaccines (PCVs) in childhood immunization programs. While the effectiveness of different vaccination schedules is well established, the additional benefit of the booster dose remains unknown. This study estimated the incidence of IPD by vaccination status in children under 18 years of age in British Columbia (BC), Canada, from 2003 to 2018. Methods: IPD cases were identified through laboratory surveillance and vaccination records obtained from provincial immunization registries. We estimated annual IPD incidence using Poisson regression, with the offset being the population at risk derived from immunization coverage rates. We calculated adjusted incidence rate ratios (aIRRs) stratified by serotype group, age, and vaccine period. Results: Among 598 IPD cases, 53.2 % were unvaccinated, 31.8 % received 2–3 primary doses and 1 booster dose (primary + booster), 15.1 % received 1–3 primary doses (primary only). Annual adjusted incidence per 100,000 was 36.1 (unvaccinated), 11.6 (primary only), and 4.6 (primary + booster). Compared to unvaccinated children, aIRRs were 0.13 (95 % CI: 0.10–0.17) for primary + booster and 0.32 (95 % CI, 0.22–0.48) for primary only. The primary + booster group had a 61 % lower incidence than the primary-only group (aIRR 0.39, 95 % CI: 0.26–0.60). These patterns were consistent across age groups (<12 months, 12–23 months, 2–4 years, 5–9 years, and 10–18 years) and serotype groups (PCV7, additional PCV13, and non-PCV13). No significant differences in aIRR were observed between PCV7 (2003−2010) and PCV13 (2010–2018) eras. Conclusions: A schedule including a booster dose was associated with a significantly lower incidence of IPD. These findings support promoting the full primary + booster (2 + 1) schedule to reduce IPD burden in children.