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Development is ongoing to increase the serotype coverage of pneumococcal conjugate vaccines. We report here the immunogenicity and safety of a new 11-valent pneumococcal conjugate vaccine (Pn-PD) in infants.In a randomized, single blind study, 154 Finnish infants received 1 of 3 regimens: 4 doses of Pn-PD at 2, 4, 6 and 12–15 months; 3 doses of the Pn-PD at 2, 4 and 6 months and 1 dose of 23-valent polysaccharide vaccine (PncPS) at 12–15 months; or 3 doses of the hepatitis B vaccine at 2, 4 and 6 months and Pn-PD at 12–15 months. Serum IgG antibodies to vaccine serotypes 1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F and 23F were measured with an enzyme immunoassay at the ages of 2, 7 and 12–15 months and at 4 or 28 days after the last vaccination. Local and systemic reactions were recorded by parents during 8 days after each dose. Serious adverse reactions were recorded during the entire study period.There was a significant increase in the IgG concentrations to vaccine serotypes after 3 doses of Pn-PD. Antibody concentrations after the primary series varied between 1.26 and 4.92 μg/ml depending on the serotype and study group. PncPS vaccine induced a better booster response than the Pn-PD, measured at 28 days after the fourth dose. IgG concentrations after the Pn-PD booster ranged between 1.60 and 9.63 μg/ml and after the PncPS booster between 4.24 and 40.54 μg/ml, depending on the serotype. The antibody concentrations after the first dose of Pn-PD administered at 12–15 months increased significantly but were lower than after the fourth dose at the same age. No significant antibody increase was measured 4 days after the vaccinations at 12–15 months. The safety profile of the vaccine was acceptable.The Pn-PD we tested was immunogenic and safe in infants.