Effectiveness of 10-valent pneumococcal conjugate vaccine estimated with three parallel study designs among vaccine-eligible children in Finland

Abstract Background Ten-valent pneumococcal conjugate vaccine (PCV10) was introduced into the Finnish National Vaccination Programme (NVP) in 9/2010. We estimated the individual-level effectiveness (VE) of PCV10 in children during eight years of vaccine implementation. Methods Data on invasive pneumococcal disease (IPD) were collected from national, population-based surveillance, and vaccination status from the vaccination register. Vaccine-eligible children were followed from six months of age until end of 2018 (born 6/2010 or later, ages 6–102 months). VE was estimated with three parallel approaches: full cohort, nested case-control and indirect cohort designs adjusting with age-group, sex and calendar year. Results VE against PCV10 serotype IPD was estimated at 93% (95% credible interval 87–97%), 98% (90–100%) and 100% (98–100%), and against PCV10-related serotypes at 46% (−13–72%), 51% (−24–79%), and 78% (−7–97%), with the full cohort, nested case-control, and indirect cohort designs, respectively. The estimated VE against non-PCV10-related (neither PCV10 nor PCV10-related) serotypes was negative but included zero effectiveness (full cohort VE −67%, −711–52%; nested case-control VE −77%, −929–59%). VE against all IPD was estimated with these two methods at 54% (24–71%) and 61% (26–79%). Over time, VE against PCV10 IPD remained stable but VE against all IPD decreased. Discussion All designs provided estimates that were concordant with each other, but those with the full cohort design were usually the most precise. PCV10 offered sustained high VE against PCV10-serotype IPD on vaccinated children during the first decade after introduction into the programme.