Jackson LA, et al. - Prior administration of 23-valent pneumococcal polysaccharide vaccine (PPSV23) in older adults blunts the opsonophagocytic antibody (OPA) response to subsequent administration of 13-valent pneumococcal conjugate vaccine (PCV13). Herein, researchers intended to investigate if a higher dose of PCV13 could mitigate this impact in adults 55 through 74 years of age. For this purpose, they compared OPA responses to a double dose of PCV13 in persons previously vaccinated with PPSV23 with responses to a single dose of PCV13 in previously vaccinated persons, and with a single dose in PPSV23 naïve persons. In older adults, a dose response to PCV13 was observed. In addition, for 9 of the 12 PCV13 serotypes evaluated, the higher response to a double dose in previously vaccinated adults was found to be non-inferior to that of a single dose in naïve adults.