A Phase IIb, Open-Label, Dose Ranging Study of 13-Valent Pneumococcal Conjugate Vaccine in Adults 55 Through 74 Years of Age Previously Vaccinated With 23-Valent Pneumococcal Polysaccharide Vaccine

The proposed phase IIb randomized, open label, dose ranging, safety and immunogenicity study will evaluate two different doses of 13-valent pneumococcal conjugate vaccine (PCV13) in two groups of participants (55 through 74 years of age). First group vaccine naïve participants will be open-label to receive a single injection of 0.5 mL PCV13. Second group of participant previously vaccinated with 23-valent pneumococcal polysaccharide vaccine (PPSV23) will be randomized 1:1 to receive two injections of 0.5 mL PCV13, one dose in each arm (Group IIA or Group IIB). Blood samples will be obtained at baseline, at one month and six months post-vaccination. The primary objectives are: to determine if two 0.5 mL doses of PCV13 are statistically significantly more immunogenic than a single 0.5 mL dose of PCV13 for at least some of the vaccine serotypes among participants 55 through 74 years of age previously vaccinated with PPSV23, as measured by serotype-specific OPA titers 28 days after study