Capsular polysaccharide vaccines today.

Polysaccharide (PS) vaccines are a relatively new class of antibacterial vaccines that have special advantages but also special problems related to their character. Several of them have proven very effective in preventing bacteremic infections caused by encapsulated bacteria such as meningococci, pneumococci and Haemophilus influenzae type b. Protective activity shows excellent correlation with serum anti-PS. However, young children often respond poorly to PS antigens and this limits the use of these vaccines in childhood. Some PS are poor immunizing agents even in adults. The practical implications of these aspects for the use and development of PS vaccines are discussed.