Abstract
Streptococcus pneumoniae is an important cause of pneumonia, meningitis and sepsis. It is an encapsulated gram-positive bacterium, and the polisaccharide capsule is the main virulence factor and the basis of the current vaccines. Free PS, however, is a T-independent antigen, not immunogenic in young children. A conjugated PS-protein vaccine has been used to immunize children, but its high…