Vaccines to prevent enteric infections.

Considerable progress has been made in the last decade in developing vaccines against the enteric infections of greatest public health importance. A quadrivalent rotavirus vaccine consisting of rhesus rotavirus vaccine (which contains serotype 3 neutralization antigen) and three reassortant viruses (rhesus virus expressing neutralization antigens of serotypes 1, 2 or 4) is undergoing placebo-controlled field trials of efficacy in the USA and in two developing countries. Two new vaccines against typhoid fever (oral Ty21a and parenteral Vi polysaccharide) have been licensed in many countries. Even newer generations of typhoid vaccines are undergoing clinical testing, including new attenuated S. typhi strains and Vi polysaccharide-carrier protein conjugate vaccines. Two inactivated oral cholera vaccines, consisting of inactivated V. cholerae O1 bacteria alone or in combination with purified B subunit of cholera toxin, each conferred 50-53% protection over 3 years in a field trial in Bangladesh where subjects were immunized with a three-dose regimen. In extensive clinical trials in adults and children in less-developed countries, an engineered live oral cholera vaccine, strain CVD 103-HgR, has been shown to be well tolerated and highly immunogenic following administration of just a single oral dose; a large-scale field trial in 70,000 subjects is underway to investigate the efficacy of this vaccine. Several candidate vaccines against Shigella and enterotoxigenic Escherichia coli are in clinical trials. Accumulating knowledge on pathogenesis of enteric infections and advances in mucosal and cellular immunology, coupled with the application of modern biotechnology, have resulted in a plethora of vaccine candidates. It is expected that in future years efforts will be directed to construct vaccines against other enteric pathogens.