History of Pneumococcal Immunization

By the year 1800, 200 years ago, the smallpox vaccine had established the principle of preventing serious disease by active immunization. In the 1940s, these whole-cell vaccines were supplanted by the next generation of pneumococcal vaccines, which consisted of the purified capsular polysaccharides (PS) of the bacteria. As early as 1891, animal experiments showed that killed pneumococci elicited protective immunity to subsequent challenge with virulent bacteria. The influenza pandemic of 1918 to 1919, together with the First World War, created a situation conducive to a highly increased incidence of pneumococcal pneumonia. Researchers administered a trivalent vaccine to 12,519 men in training at the United States. The results of the trials with the killed whole-cell vaccines were considered very encouraging at the time. Even a 30% reduction in numbers of cases of lobar pneumonia was welcomed because there were no alternative prevention measures. The experimental research of Avery, Heidelberger, and Goebel in the 1920s formed the essential links between pneumococcal capsules, their serotype specificity, and the identity of the capsules with PS that could be isolated from the bacterial cultures by chemical means. Despite recommendations for routine of pneumococcal immunization at-risk populations, the uptake of the vaccine was relatively slow. Nearly 10 years after the licensure of PS vaccine in the United States, only 10% of persons for whom the vaccine was recommended had ever been immunized. Protection against pneumococcal bacteremia, provided by the 23-valent PS vaccine, wanes over a period of 3 to 5 years, particularly in older people.