Proceedings of The First Current Topic in Infectious Diseases
Overview of Conjugate Pneumococcal Vaccine: Serotype Coverage, Efficacy and Status of Usage in other Countries
Streptococcus pneumoniae remains a major cause of morbidity and mortality even in the developed countries. It is one of the commonest causes of community-acquired pneumonia, bacteraemia, meningitis, acute otitis media, sinusitis, and postsplenectomy sepsis.6 Currently available vaccines target the polysaccharide capsule, whose antiphagocytic property is a major virulence factor. Of the 90 described capsular types, the 23 commonest types are included in the polysaccharide vaccine, which provides coverage against 80% to 90% of bacteraemic isolates.7,8 The polysaccharides, however, are poorly immunogenic in children less than two years of age that are most susceptible to invasive pneumococcal infections. Pneumococcal polysaccharides are therefore conjugated to proteins to improve their immunogenicity in young children and infants. A heptavalent conjugate pneumococcal vaccine was licensed in 2000 in the United States, which contains serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. CRM197, a non-toxic variant of diphtheria toxin, is used as the protein conjugate. These seven serotypes accounted for 86% of bacteraemia, 83% of meningitis, and 65% of acute otitis media in children less than six years of age in the United States. In a randomized, double-blinded clinical trial in which ~37,000 children were recruited, the heptavalent vaccine is ~100% effective in preventing invasive pneumococcal infections caused by vaccine serotypes and 89% against all serotypes. There is a 7.0%-22.8% reduction in the incidence of otitis media and a 5.3% reduction in antibiotic use in the vaccinees. The vaccine is presently licensed for use in infants older than six weeks and is given at two, four, six months, with a booster dose at 12-15 months. It is recommended for children less than 23 months old; for children aged 24-59 months, it should be considered for those who are predisposed to severe pneumococcal disease. A 40%-50% reduction in nasopharyngeal pneumococcal carriage of vaccine serotypes is found in field trials of a 9-valent conjugate vaccine.
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