The included studies had to report the proportion of children with ELISA antibody levels of at least 35μg/mL after primary infant immunisation.
Eligible studies were RCTs that compared two with three primary immunisations (type B) and single-arm trials (three primary immunisations) and compared antibody levels after two and after three immunisations in the same patients (type A). Studies of children immunised after six months were excluded. Three pneumococcal conjugate vaccines (PCV7, PCV10 and PCV13) licensed in Europe and USA were eligible for inclusion in this study. The difference between the proportion of participants with antibody levels of at least 0.35μg/mL after two and three doses of PCV was chosen as an endpoint.
Studies were conducted in Germany, Poland, Spain, Denmark, Norway, Slovakia, Sweden, Fiji, Korea, Israel and The Gambia. RCTs used a vaccination schedule of two, four and six months. Schedules in single-arm trials varied. Antibody levels were evaluated one month after each vaccination for all studies.
The authors did not state how many reviewers were involved in study selection.