S. pneumoniae bacteria are serotyped based on the polysaccharides in the outer capsule of the bacteria. Serotypes vary in how common they are and in what percentage of pneumococcal disease they cause.
Among the PCV vaccines, PCV13 includes serotypes: 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F. PCV15 includes all PCV13 serotypes plus 22F and 33F. PCV20 includes all PCV15 serotypes plus 8, 10A, 11A, 12F, and 15B. PPSV23 vaccine does not contain serotype 6A or 19A, but contains 19 other serotypes present in PCV20, plus serotypes 2, 9N, 17F, and 20.