A CONTROLLED FIELD TRIAL OF ACETONE-DRIED AND INACTIVATED AND HEAT-PHENOL-INACTIVED TYPHOID VACCINES IN BRITISH GUIANA.

In 1960, some 72 000 schoolchildren in British Guiana participated in a controlled field trial of typhoid fever vaccines that was supported in part by the World Health Organization. The children were divided into three groups each receiving two doses, one of acetone-dried and inactivated vaccine, the second of heat-phenol-inactivated vaccine, and the third (control group) of tetanus toxoid. They were followed up over 3 1/2 years, during which time 99 cases of typhoid fever occurred in the control group, 6 in the acetone-dried vaccine group, and 26 in the heat-phenol vaccine group. Attack rates of the same order of magnitude were observed among 10 000 other children divided into the same three groups but given only one inoculation.The vaccines used were the same as those tested in a similar trial in Yugoslavia, and, although the attack rates in British Guiana were considerably lower in all groups than those in Yugoslavia, the findings in the two trials are in general agreement and indicate that acetone-dried vaccine confers greater protection than vaccine prepared from the same strains but inactivated by heat-phenol.