Other Pneumococcal Vaccines

The PPV Vaccine

There are 90 different serotypes of pneumococci bacteria each of which has a different polysaccharide capsule. The differences in this capsule often determine how virulent a given serotype is. The polysaccharides on the surface of the capsule protect the bacteria from the immune system by providing a barrier to killing.

Even though there are a total of 90 serotypes, many of these do not cause severe disease. Eighty-eight percent of disease worldwide is caused by 23 serotypes. Portions of the polysaccharide capsule from these 23 serotypes are included in the pneumococcal polysaccharide vaccine (PPV). Some of the serotype capsules have commonalities with others. As a result, it is possible that a vaccine will be partially effective against serotypes not specifically included in the vaccine. In order to be sure that the vaccine will be effective against a particular serotype however, capsular sugars from that serotype need to be included in the vaccine.

Polysaccharides are poorly immunogenic molecules and therefore they cannot induce immunity in young children. The PPV vaccine is effective and recommended in many countries for the elderly and for high risk groups such as those who are immunocompromised.

Future Vaccines

Research is being done to develop novel vaccines for pneumococcal disease. Much of this research is centered on finding proteins that are expressed on the surface of the pneumococcus that could provide recognizable targets for the immune system. As previously discussed, proteins are far more immunogenic than polysaccharides. In addition, many proteins are common to all serotypes, so there is potential to develop a protein based vaccine that is effective against all serotypes of disease.