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

A controlled field trial on some 584 000 people in an endemic cholera El Tor area in the Philippines demonstrated that cholera vaccines gave moderate protection of short duration. Injection of a single dose of vaccine prepared from either Vibrio cholerae or El Tor vibrios gave over 50% protection for the first 2 months. The immunity conferred by the V. cholerae vaccine declined rapidly after 3 to 4 months. The effectiveness of the El Tor vaccine continued for 6 months. An oil-adjuvant vaccine prepared from V. cholerae conferred an equally high degree of protection for a longer period of time, but, owing to severe vaccination reactions, its use could not be recommended.