Polysaccharide vaccine The polysaccharide vaccine consists of purified polysaccharides from 23 serotypes (1, 2, 3, 4, 5, 6b, 7F, 8,9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F and 33F) (17). 23 valent pneumococcal polysaccharide vaccine (PPV) was licensed in 1983, replacing the 14-valent vaccine introduced in 1977. Vaccine serotypes account for 86% of bacteremia, 83% of meningitis & 65% of AOM among <6 yrs Pneumovax 23 produced by Merck Research Laboratories, USA. Immunity is induced primarily through stimulation of B-cells which release IgM (17) without the assistance of T cells (18). (17)Pletz MW, Maus U, Krug N, Welte T, Lode H (September 2008). "Pneumococcal vaccines: mechanism of action, impact on epidemiology and adaption of the species" . Int. J. Antimicrob. Agents 32 (3): 199–206. (18)Stein KE (June 1992). "Thymus-independent and thymus-dependent responses to polysaccharide antigens" . J. Infect. Dis. 165 (Suppl 1): S49–52.