Frozen stored Leishmania tropica vaccine: The effects of dose, route of administration and storage on the evolution of the clinical lesion. Two field trials in the Israel Defense Forces

The first field trial of frozen vaccine against cutaneous leishmaniasis yielded a 100% take rate and a high ulceration rate at a dose of four million units. Two further trials were designed to investigate differences in response rates on the basis of duration of storage, sex of vaccinee, vaccination dose and method of administration.257 soliders (151 males and 106 females) were inoculated in 1978 with an isolate of Leishmania tropica major that had been stored at the temperature of liquid nitrogen for 11 months before use. Those inoculated with an intradermal jet injector and those receiving half a million units by conventional injection yielded very low take rates. For those receiving two million and one million units, no difference in response was demonstrated between males and females or between doses. The over-all take rate for these groups after six months of follow-up was 71·6% with an ulceration rate of only 23·7%.In a subsequent trial in 1979, 131 men were inoculated with one of two frozen isolates of L. tropica major that had been stored for 11 and 18 months, respectively, at doses of either two million or four million units. The take rate after 12 months of follow-up was 91% and 93% for the four and two million units dose, respectively. The corresponding ulceration rates were 39·5% and 25%. The lesions produced by the higher dose developed more rapidly than those produced by the lower dose. The ability of the parasites to produce lesions rapidly with high ulceration rates appears to decline during prolonged storage, even in the frozen state.