Preparation and laboratory tests of oil-adjuvant cholera vaccine.

In a search for cholera vaccines of improved efficacy, agar-grown strains of classical Vibrio cholerae were killed with formol and emulsified with Arlacel A in mineral oil; the final vibrio concentration was adjusted to 2 x 10(9) vibrios per adult dose (equal proportions of Inaba and Ogawa types).There was an unexplained discrepancy between determinations of the vibrio content, by cell counting and opacity measurements, and of the antigen content, by nitrogen measurements and the complement-fixation test.The potency of the vaccine, estimated by the mouse-protection test, was about 5 times that of the International Reference Preparations of Cholera Vaccine. A new potency test, the "maternal-immunity" test in infant rabbits, did not give quantitative results but suggested a somewhat higher potency for the vaccine.The protective effect 6 months after vaccination, as determined by agglutinin titres in the sera of volunteers, was still high, confirming the results of a field trial of the vaccine. However, local reactions (indurations) were observed in a considerable proportion of vaccinees in the field trial. Histopathological examination of tissue from the site of the reactions revealed them to be due to a combination of foreign-body reactions and local hypersensitivity.