The 23-valent pneumococcal polysaccharide vaccine (PPSV23) contains antigens from the 23 most virulent of the 83 subtypes of S pneumoniae (1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F, 33F).