Long-term impact of 10-valent pneumococcal conjugate vaccination on invasive pneumococcal disease among children in Finland.

BACKGROUND: The ten-valent pneumococcal conjugate vaccine (PCV10) was introduced into the Finnish National Vaccination Programme (NVP) in September 2010. The impact of PCV10 vaccination against invasive pneumococcal disease (IPD) in vaccine-eligible children has been high. We evaluated the long-term impact of PCV10 vaccination against IPD in vaccine-eligible and older, unvaccinated children six years after PCV10 introduction with a special focus on cross-protection against PCV10-related serotypes (serotypes in the same serogroups as the PCV10 types).

METHODS: We used data on IPD from the national, population-based surveillance. A target cohort of vaccine-eligible children (born June 2010 or later) was followed from 3 months of age until the end of 2016. For the indirect effect, another cohort of older PCV10-ineligible children was followed from 2012 through 2016. IPD rates were compared with those of season- and age-matched reference cohorts before NVP introduction.

RESULTS: Among vaccine-eligible children, the incidence of all IPD decreased by 79% (95% CI 74-83%). There was a statistically significant reduction in the incidence of 6A IPD, but for 19A, the reduction was non-significant and the incidence of 19A increased towards the end of the study period in the older vaccine-eligible children. The increase in non-PCV10 related serotypes was non-significant. In the unvaccinated older children, the incidence of all IPD decreased by 33% (95% CI 8-52%) compared to the reference cohort, and there was no impact on serotype 6A or 19A IPD.

CONCLUSION: Overall, the impact of PCV10 vaccination on IPD was high in vaccine-eligible children, with a major reduction in vaccine-type disease, and without notable replacement by other serotype groups. Our data suggest that PCV10 results in long-lasting direct cross-protection against 6A IPD. For 19A, no net reduction was observed six years after NVP introduction in the vaccine-eligible cohort. The indirect impact on IPD in unvaccinated children sustained.