Pneumococcal conjugate vaccines
Diseases caused by Streptococcus pneumoniae (S. pneumoniae or pneumococcus) are a major public health problem worldwide. Serious diseases that are often caused by pneumococci include pneumonia, meningitis and febrile bacteraemia; otitis media, sinusitis and bronchitis are more common but less serious manifestations of infection. In 2005, WHO estimated that 1.6 million people die of pneumococcal disease every year; this estimate includes the deaths of 0.7-1 million children aged less than 5 years, most of whom live in developing countries. The magnitude of the burden of pneumococcal disease among elderly people in developing countries is undefined. In the developed world, children aged less than 2 years and the elderly people carry the major burden of disease. HIV infection and other conditions associated with immune deficiency greatly increase the likelihood of contracting pneumococcal disease. The growing resistance of S. pneumoniae to commonly used antibiotics underlines the urgent need for vaccines to be used to control pneumococcal disease.
Antibodies to capsular polysaccharide antigens provide serotype-specific protection against serious infections, and the pneumococcal vaccines are designed to cover the serotypes most commonly associated with severe pneumococcal disease. Currently, a polysaccharide vaccine covering 23 serotypes (23-valent) and a 7-valent polysaccharide-protein conjugate vaccine are marketed internationally. Both vaccines are considered very safe.