Pneumococcal illness is still a public health concern in adults. In people  aged 50 years, the safety and immunogenicity of two formulations of 15-valent pneumococcal conjugate vaccination (PCV15) including 13 serotypes contained in 13-valent pneumococcal conjugate vaccine (PCV13) plus two extra serotypes were studied. 690 individuals were given a single dose of PCV15 Formulation A, PCV15 Formulation B, or PCV13 and were monitored for 14 days after immunisation for safety. Geometric mean titers (GMTs) of serotype-specific opsonophagocytic activity (OPA) and geometric mean concentrations (GMCs) of immunoglobulin G (IgG) were evaluated immediately before and 30 days after immunisation. The IgG GMCs and OPA GMTs at baseline were comparable among immunisation groups. Both PCV15 formulations elicited serotype specific antibodies to all 15 serotypes in the vaccine 30 days after immunisation. IgG GMCs and OPA GMTs in PCV15 receivers were non-inferior to those assessed in PCV13 recipients for shared serotypes and superior for PCV15-specific serotypes. In general, Formulation B elicited stronger immunological responses than Formulation A.

Both novel formulations of PCV15 demonstrated acceptable safety profiles and elicited serotype-specific immune responses equivalent to PCV13 in healthy individuals 50 years of age.