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

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.