Diseases caused by Streptococcus pneumoniae (the pneumococcus) are a major public health problem worldwide. In the developing world young children and the elderly are most affected; it is estimated that about one million children die of pneumococcal disease every year. Streptococcus pneumoniae is an encapsulated bacteria with a polysaccharide capsule an essential factor in virulence. About 90 distinct pneumococcal serotypes have been identified throughout the world, with a small number of these serotypes accounting for most disease in infants. Pneumococci are transmitted by direct contact with respiratory secretions from patients and healthy carriers. Serious pneumococcal infections include pneumonia, meningitis and febrile bacteraemia; otitis media, sinusitis and bronchitis are more common but less serious manifestations. Pneumococcal resistance to antimicrobials is a serious and rapidly increasing problem worldwide.
Antibodies to capsular polysaccharide antigens of S. pneumoniae provide serotype-specific protection against pneumococcal infections. Pneumococcal vaccines are designed to cover the serotypes most frequently associated with severe pneumococcal disease. Pneumococcal polysaccharides are T-cell independent antigens and thus are:
- poorly immunogenic in those aged <2 years; and
- fail to induce immune memory.
Two classes of pneumococcal vaccines are currently available, one based on polysaccharides and the other based on polysaccharides conjugated to a carrier protein. The polysaccharide vaccine consists of purified capsular polysaccharides from the 23 serotypes causing about 90% of invasive pneumococcal infection in industrialized countries. Responses are age-dependent and serotype-dependent.
Pneumococcal conjugate vaccines contain polysaccharides from 7 serotypes covering 65–80% of serotypes associated with invasive pneumococcal disease among young children in western industrialized countries. The polysaccharides are conjugated to a carrier protein which makes them more immunogenic and effective in protecting against infection, in particular in young children less than 2 years of age. Furthermore, the vaccine protects against both systemic and mucosal infection and prevents nasopharyngeal colonization, thereby reducing transmission in the community.
Pneumococcal vaccine standardization
WHO recommendations for pneumococcal conjugated vaccines were adopted by the Expert Committee for Biological Standardization (ECBS) in 2003 and subsequently revised and adopted by ECBS at their 60th meeting in 2009.
Recommendations to assure the quality, safety and efficacy of pneumococcal conjugate vaccines-proposed replacement of TRS 927, Annex 2, ECBS, October 2009
No WHO reference materials for pneumococcal vaccines are currently available.
WHO/Health Canada Consultation on serological critera for evaluation and licensing of new Pneumococcal vaccines, Ottawa, Canada, 7-8 July 2008
WHO Workshop on Standardization of Pneumococcal Opsonophagocytic Assay, Geneva, Switzerland 25-26 January 2007
Prequalified pneumococcal (conjugate) vaccines
Pneumococcal (conjugate) vaccines are prequalified for procurement by UN organization.