Polysaccharide vaccines for prevention of encapsulated bacterial infections: Part 1

Protective immunity to encapsulated bacteria involves an antibody response to a polysaccharide (PS) antigen, interactions with T and B lymphocytes, and host defense mechanisms. PS vaccines, such as those developed against Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b, and Salmonella typhi, prevent infection by inducing an immune response against specific capsular polysaccharides. These vaccines, however, provided little protective immunity in infants and young children. The development of glycoconjugate vaccines overcame many limitations associated with PS vaccines by eliciting a quantitatively and qualitatively different immune response. Alternative strategies intended to enhance an immune response in infants include maternal immunization with PS or conjugate vaccine and hormone treatment during the critical period of neonatal development.