Immunogenicity and safety of a 13-valent pneumococcal conjugate vaccine in adults 18-49 years of age, naive to 23-valent pneumococcal polysaccharide vaccine. 
Based on the success of vaccination with pneumococcal conjugate vaccines (PCVs) in children, recent studies have focused on PCVs in adults.  Data from a randomized, double-blind study comparing the immunogenicity, tolerability, and safety of the 13-valent PCV (PCV13) and the 23-valent pneumococcal polysaccharide vaccine (PPSV23) in PPSV23-naive adults 60-64 years of age have been published.  The same study also included a cohort of adults aged 18-49 years that received open-label PCV13.  The purpose of this cohort was to examine the immunogenicity, safety, and tolerability of PCV13 in adult subjects 18-49 years of age compared with adults 60-64 years of age for whom PCV13 is approved.  Adults naive to PPSV23 were grouped by age into 2 cohorts: 18-49 years (n=899; further stratified by age into 3 subgroups 18-29, 30-39, and 40-49 years) and 60-64 years (n=417).  All subjects received 1 dose of PCV13.  In both age groups, immunogenicity was assessed by antipneumococcal opsonophagocytic activity (OPA) geometric mean titers (GMTs) and IgG geometric mean concentrations (GMCs) 1 month after vaccination.  Safety and tolerability were evaluated.  In adults aged 18-49 years, OPA GMTs and IgG GMCs were noninferior for all 13 serotypes and statistically significantly higher for all except 1 serotype (OPA GMT) and 5 serotypes (IgG GMCs) compared with adults 60-64 years.  Immune responses were highest in the youngest age subgroup (18-29 years).  Local reactions and systemic events were more common in adults 18-49 years compared with 60-64 years and were self-limited.  Immune responses to PCV13 are robust in adults ≥18 years of age, with highest responses observed in the youngest subgroup.  Based on its safety and immunologic profile, PCV13 may serve an important therapeutic role in younger adults, particularly those with underlying medical conditions who have an increased risk of serious pneumococcal infections.