Live oral cholera vaccine: report of a trial on human volunteer subjects.

Earlier laboratory studies on the possibility of basing a live oral cholera vaccine on a naturally avirulent strain of El Tor vibrio have shown that the strain is capable of multiplication in the gastrointestinal tract of rabbits resulting in the production of antibacterial and antitoxic immunity. In order to examine the safety and immunogenic value for human use of this proposed vaccine, a systematic trial has been carried out on 25 human volunteers. Following oral administration of the vaccine after neutralization of gastric acidity, the volunteers developed statistically significant increases in their vibriocidal antibody level. Copro-antibodies could also be demonstrated in stool samples within a week of vaccination Serum and copro-antibody levels persisted unchanged during the periods of observation of 6 and 3 months, respectively. None of the volunteers suffered any ill effect during the course of the trial. It has been concluded that the proposed vaccine is safe for human use and likely to protect against infection, although its protective value has still to be confirmed in a field trial.