Protective activity of cholera vaccines against E1 Tor cholera vibrios

With the advent of epidemic El Tor cholera there has been concern about the value of cholera vaccine prepared from classical cholera strains.Using a recently developed mouse protection test, the authors have determined the protective activity of five commercial vaccines against strains of epidemic El Tor and classical cholera vibrios. Both Ogawa and Inaba types of each kind of vibrio were used. With each vaccine, protection against El Tor vibrios was as good as that against classical cholera vibrios. There was, however, a greater than tenfold difference in the potency of the vaccines.The findings support the use of cholera vaccine for immunization against El Tor cholera and show that there are wide variations in the mouse-measured potency of lots of vaccine. The significance of the findings must await results of controlled field trials.

PRELIMINARY STUDIES ON THE DEVELOPMENT OF A LIVE ORAL VACCINE FOR ANTI-CHOLERA IMMUNIZATION

Since humoral anti-O antibodies play little part in protective immunity against cholera, and the infecting organisms remain limited in the gut, effective prophylaxis will require the production of active immunity in cells of the mucous membrane of the intestinal canal. It has not been possible to achieve this objective satisfactorily by injections of killed cholera cultures. In laboratory studies for a solution of the problem it has been shown that Vibrio cholerae and V. El Tor strains possess identical somatic antigens. El Tor vibrio strains isolated from surface water in an area free from cholera were found to be of low pathogenicity while retaining full antigenicity. Administration of these strains to mice and rabbits was shown to confer protection against subsequent challenge with both V. cholerae and pathogenic V. El Tor strains. On the basis of the data presented a case has been made for a viable vaccine prepared from a suitable non-pathogenic El Tor strain, for administration by the oral route. It may be expected that such a vaccine will establish an effective immunity through protection of the local susceptible cells of the intestines as a result of subclinical infection. The safety and protective value of the vaccine remain to be verified in human volunteers before it can be chosen for field trials.