Short-chain oligosaccharide protein conjugates as experimental pneumococcal vaccines

Streptococcus pneumoniae remains a major cause of acute respiratory infections worldwide and is responsible for approximately 1 million childhood deaths each year. Despite the widespread use of antibiotics, the mortality and morbidity of pneumococcal disease remains high. Therefore, effective vaccines to prevent pneumococcal disease are needed. Bacterial vaccine development in general follows a similar track starting from large, rather crude vaccines (whole live, attenuated pathogen) towards smaller, better defined subunit vaccines. Ultimately, this track leads to the development and evaluation of minimal, highly defined subunit vaccines, based on a collection of single protective epitopes. This mini-review deals with capsular saccharide based vaccines. After a short overview of the development of pneumococcal vaccines from the 23 - valent polysaccharide vaccines to polysaccharide-protein conjugate vaccines, it focuses on the vaccine potential of synthetic oligosaccharides, conjugated to carrier proteins.