Childhood pneumococcal conjugate vaccination in Aotearoa New Zealand and the delayed indirect effects on older populations: a population-based surveillance cohort study

BACKGROUND: In Aotearoa New Zealand (NZ) there have been multiple changes to the childhood pneumococcal vaccine schedule since 2008 when PCV7 was first introduced. Most recently PCV13 was reintroduced in late 2022 after 5 years of PCV10. In the present study, we investigate the shifts in invasive pneumococcal disease (IPD) incidence rates attributed to PCV-specific serotypes. METHODS: We report PCV-specific trends in IPD, PCV-specific vaccine impact (VI) by age group, and report the timing for expected reductions in PCV13-specific (non-PCV7 serotypes) IPD for children under 5 and adults 65 or over. FINDINGS: IPD incidence rates in NZ are at historically high levels for adults 65 or over, while rates for children under 2 and 2-4 years old have dropped significantly since the re-introduction of PCV13. Māori and Pacific peoples are experiencing the highest rates of IPD since 2009. The percent of IPD cases attributed to PCV13-specific serotypes has decreased across all age groups, while the percent of cases attributed to PCV20-specific serotypes has increased for most age groups. The VI of PCV13 was 79% (95% CI 59-90%) for children under 2 years of age. Similarly, the timing of a 50% decrease in risk for PCV13-specific (non-PCV7 serotypes) IPD was very rapid for children under 2 (within 1 year) and delayed for adults. INTERPRETATION: Though overall incidence rates of IPD remains very high, this is driven primarily by non-PCV serotypes. The VI for all PCVs remains high, especially for younger cohorts. Delayed indirect benefits are continuing to be experienced by older populations.