Development of oral vaccines against cholera and enterotoxinogenic Escherichia coli diarrhea.

An oral cholera vaccine consisting of the immunogenic but completely nontoxic B subunit of cholera toxin in combination with heat- and formalin-killed cholera vibrios has been developed. This vaccine, which was designed to evoke antitoxic as well as antibacterial intestinal immunity, has in extensive clinical trials including a large field trial been shown to confer, without any side-effects, protection against cholera lasting for at least 3 years. The vaccine also induced protection of shorter duration against diarrhea caused by enterotoxinogenic Escherichia coli (ETEC). Significant progress has also been made recently using recombinant DNA techniques towards development of a live attenuated oral cholera vaccine. Furthermore, new knowledge about virulence factors and protective antigens of ETEC has given promise that an effective oral ETEC vaccine may soon be developed combining a B subunit toxoid with inactivated ETEC expressing the most important colonization fimbrial antigens.