A CONTROLED FIELD TRIAL OF THE EFFECTIVENESS OF ACETONE-DRIED AND INACTIVATED AND HEAT-PHENOL-INACTIVATED TYPHOID VACCINES IN YUGOSLAVIA.

In 1954-60 a Yugoslav Typhoid Commission showed in the first controlled field trial of typhoid vaccines, carried out in Osijek, Yugoslavia, that heat-phenol-inactivated typhoid vaccine gave a relatively high and long-lasting immunity. However, this liquid vaccine preparation was unstable and laboratory potency tests were inconclusive, and it was therefore decided that stable, dried, heat-killed, phenol-preserved vaccine be tested together with an acetone-inactivated and -dried vaccine in controlled field trials, supported in part by the World Health Organization, in Yugoslavia and British Guiana.This is report on the controlled trials organized in two Yugoslav towns, Bitola and Pristina. Three comparable groups were formed by random allocation of vaccines among 45 497 volunteers in the two towns. In each town one group received heat-phenol vaccine, the second group acetone-dried vaccine and the third (control) group tetanus toxoid. Two doses were given four weeks apart in the spring of 1960 and the vaccinated persons were followed up for 2 1/2 years. The effectiveness of the vaccines was measured by comparing typhoid morbidity rates in the three groups. It was found during an outbreak of typhoid fever in Pristina two years after primary vaccination that both the acetone-dried and the heat-phenol vaccines were effective, the former being superior.