A SEVEN-YEAR FIELD TRIAL OF TWO TYPHOID VACCINES IN GUYANA

Abstract

In 1960 about 72,000 Guyanese schoolchildren, aged five to fifteen years, were divided into three similar groups, one of which acted as a control and was given tetanus toxoid, the second was given an acetone-killed typhoid vaccine, and the third a heat-killed-phenolised typhoid vaccine. Two subcutaneous doses of 0.5 ml. of reconstituted vaccines were given five weeks apart. An additional 10,000 children received one dose only. The incidence of typhoid fever, diagnosed by the bacteriological isolation of Salmonella typhi, was followed for seven years after vaccination. In those given two doses, 146 cases of typhoid occurred in the control group and 16 and 49 in the acetone and heat-phenol typhoid vaccine groups, showing protection-rates of 88% and 65%, respectively. In those given one dose of vaccine the protection was somewhat greater, 22 cases occurring in the control group and 1 and 4 in the groups given the acetone and heat-phenol vaccines, respectively. Protection showed little diminution until the fifth year after vaccination.