Streptococcus pneumoniae (pneumococcus) is a leading cause of serious illness among children worldwide . Before universal infant immunization with pneumococcal conjugate vaccine in the United States, S. pneumoniae caused approximately 17,000 cases of invasive disease each year among children younger than five years of age, including 700 cases of meningitis and 200 deaths . It was the most frequent cause of bacteremia, bacterial pneumonia, bacterial meningitis, sinusitis, and acute otitis media . Since pneumococcal conjugate vaccine was added to the routine childhood immunization schedule in the United States, the incidence of invasive pneumococcal disease has declined by 60 to 90 percent in children younger than two years. (See 'Efficacy and effectiveness' below.)
The use of pneumococcal conjugate vaccines in children will be presented here. Pneumococcal polysaccharide vaccines in children, pneumococcal vaccination in adults, and the impact of universal infant immunization with pneumococcal conjugate vaccine in the United States are discussed separately. (See "Pneumococcal (Streptococcus pneumoniae) polysaccharide vaccines in children" and "Pneumococcal vaccination in adults" and "Impact of universal infant immunization with pneumococcal (Streptococcus pneumoniae) conjugate vaccines in the United States".)
The surface capsular polysaccharide of S. pneumoniae provokes a type-specific protective immune response and serves as the basis for serotyping of these organisms. More than 90 different pneumococcal serotypes have been identified. Serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F are the most prevalent in children, accounting for between 60 and 80 percent of infections, depending upon the area of the world. (See "Microbiology and pathogenesis of Streptococcus pneumoniae", section on 'Capsule'.)
It is not currently possible to include all >90 serotypes in a polysaccharide or polysaccharide-conjugate vaccine. Pneumococcal polysaccharide vaccines representing subgroups of the 14 and 23 most prevalent serotypes causing invasive disease were developed in the 1970s and 1980s (PPSV14 and PPSV23, respectively) . Pneumococcal polysaccharide vaccines are discussed separately. (See "Pneumococcal (Streptococcus pneumoniae) polysaccharide vaccines in children" and "Pneumococcal vaccination in adults".)
Polysaccharide vaccines are poorly immunogenic in children younger than two years [4,5], the age group with the highest incidence of invasive disease . However, conjugation of an immunogenic nonpneumococcal protein (carrier protein) to individual pneumococcal polysaccharides elicits a T cell-dependent memory response and increases the effectiveness of the vaccine during the first two years of life. Carrier proteins for pneumococcal conjugate vaccines include CRM197 (a nontoxic mutant of diphtheria toxin) and OMP (the outer membrane protein complex from Neisseria meningitidis). Conjugate vaccines including a pneumococcal protein are in development with the goal of expanding protection beyond capsular type.