On Jul. 1, 1983, two enhanced pneumococcal polysaccharide vaccines were licensed (Pneumovax 23 by Merck on Jul. 11 and Pnu-Imune 23 by Lederle on July 21). These vaccines included 23 purified capsular polysaccharide antigens of Streptococcus pneumoniae and replaced the 14-valent polysaccharide vaccine licensed in 1977.