Role of bacterial vaccines in prevention of respiratory infections with special reference to pneumococcal vaccines.

There are significant differences between polymicrobial and monomicrobial vaccines. Polymicrobial vaccines clearly cannot prevent all bacterial diseases and their indications are ill-defined, but might be better established by controlled clinical trials in which these preparations are tested against placebos. The pneumococcal vaccine represents real progress in reducing the incidence and mortality of pneumococcal infection in patients with either a high risk of contracting such an infection or a high risk of a fatal outcome if infection occurs.