Pneumococcal vaccine.

Streptococcus pneumoniae or pneumococcus is a major pathogen causing meningitis, pneumonia, other invasive infections, and the common infections acute otitis media and sinusitis. The major virulence factor is the polysaccharide capsule, present as one of approximately 90 serotypes. Anticapsular antibodies protect against infection. In 1977 and 1997, vaccines composed of purified capsular polysaccharide from 14- and 23-capsular types, respectively, were licensed for use in those children 2 years of age or older who are at increased risk for invasive pneumococcal infection. These vaccines have limited immunogenicity in infants and young children. Pneumococcal conjugate vaccines in which capsular polysaccharides from a limited number of serotypes are covalently linked to a protein carrier have recently been developed. In preliminary reports of randomized, double-blind control studies, a heptavalent vaccine administered as a series of infections to normal infants was efficacious in the prevention of invasive infections, episodes of lobar pneumonia, and acute otitis media caused by vaccine serotypes.