The purpose of this prospective randomized study is to assess the safety, post-vaccination antibody response, and memory response to a subsequent polysaccharide challenge of varying doses of PCV7 compared with the standard dose of PPV23 in immunocompetent adults 70-79 years of age who were previously vaccinated with PPV23 at age 65 years or above and at least 5 years previously. The study will be conducted among a total of 220 persons recruited from GHC and the Seattle VAMC. Participants will be randomized into one of 5 study groups with 44 participants per group. The antigen content of PCV7 will be varied by administration of different volumes of the licensed pediatric formulation of that vaccine. Four groups will receive one of four volumes (0.1 mL, 0.5 mL, 1.0 mL, 2.0 mL) of the licensed pediatric formulation of PCV7 followed 12 months later by administration of a challenge 0.1 mL dose of PPV23 to assess the induction of immunologic memory. The comparison group will receive the standard 0.5 mL dose of PPV23 following 12 months later by administration of a 0.1 mL dose of PPV23.