The pneumococcus: carriage, disease and conjugate vaccines.

Modern biotechnology has made possible the rapid development and introduction into clinical care of a wide spectrum of potent antimicrobial agents. However, the battle against Streptococcus pneumoniae (pneumococcus) has remained fierce, as acquisition of resistance is even more rapid and these antimicrobial agents are rendered ineffective. Obtaining appropriate antibiotic treatment for severe invasive pneumococcal infections is now a major challenge in many regions of the world. The ground-breaking success of Haemophilus influenzae type b (Hib) conjugate vaccine has brought hope for the conquest of other capsulate bacteria. Recent results of efficacy trials of a heptavalent pneumococcal conjugate vaccine bring hope that protein conjugate vaccines will have a similar impact on pneumococcal disease. These multivalent vaccine formulations include pneumococcal serotypes that most often acquire antibiotic resistance and there is hope that the widespread application of these vaccines will decrease the incidence of multi-drug-resistant infections. The potential reduction of pneumococcal disease could even extend to unimmunised younger siblings and the elderly residing with immunised young children, through its herd effect. However, in view of the multiplicity of serotypes and the biology of the pneumococcus, optimism must be tempered by caution.