Response of man to infection with Vibrio cholerae. II. Protection from illness afforded by previous disease and vaccine.

Human immunity acquired after cholera or provided by cholera vaccines was evaluated. Previous diarrhea caused by infection with Vibrio cholerae induced complete protection against diarrhea after a second challenge with the homologous organism four to 12 months later; vibrios were recovered from only one of 21 patients challenged with the homologous organism. Four of six other men challenged again after the same interval with a heterologous serotype developed mild diarrhea. A whole-cell Inaba vaccine, given either parenterally or orally, produced significant protection against excretion of the organisms and lowered the incidence and severity of diarrhea; the vaccine was more effective when administered parenterally. A partially purified toxoid vaccine also provided some protection. An individual's immunity either to infection or to diarrhea was not correlated with his serum titer of vibriocidal antibody or his serum titer of antitoxin. Immunity, either naturally acquired or vaccine-induced, appeared to be directed against the vibrio rather than against the toxin. At present, cholera vaccines are less effective than previous infection in prevention of subsequent illness.