[Polysaccharide subunit vaccines]

The polysaccharide capsules of many germs (pneumococcus, meningococcus, Haemophilus b, salmonella, etc.) can induce synthesis of protective antibodies in man. The development of many vaccines has been based on this phenomenon. Unfortunately, the polysaccharide antigens cannot trigger an immune response before the age of 2 years. In addition, they do not induce an anamnestic response, as do protein antigens. Great progress has been made by conjugating these polysaccharide antigens with protein antigens (tetanus and diphtheria antigens in particular). The resulting novel antigen induces a thymus-dependent response in man, leading to immunogenicity from the first weeks of life, and to a higher and more durable antibody response. On subsequent administration, such conjugated vaccines provoke a booster effect. In practice, the anti-Haemophilus b conjugated vaccine has obtained spectacular results in prevention of meningitis, with an effectiveness close to 100%. Results of the first trials of conjugated anti-pneumococcal vaccines suggest that they may constitute an effective new means of combating the emerging pneumococcal strains resistant to penicillin.