A controlled field trial of the effectiveness of monovalent classical and El Tor cholera vaccines in the Philippines.

Monovalent Ogawa and Inaba vaccines prepared from classical and El Tor strains of Vibrio cholerae were field-tested in Negros Occidental, Philippines, where cholera El Tor, serotype Ogawa, is endemic. The monovalent classical Ogawa and Inaba vaccines were of the same lots as those tested in East Pakistan in 1968-69. The results indicated that all four types of vaccine tested offered significant degrees of protection varying from 58% to 71%. The Ogawa vaccines were slightly, though not significantly, more protective than the Inaba vaccines against disease caused by Ogawa. The biotypes of the vaccine strains were found to be of no consequence.