Studies on Tularemia. V. Immunization of Man

Abstract

Eight hundred and nine individuals including 163 laboratory workers received 1 or more prophylactic injections of phenolized or acetone-extracted tularemia vaccine. Before administration of vaccine, a careful clinical history, skin test, and agglutinin titration were done to detect individuals who had experienced previous tularemic infection. Such individuals were not vaccinated because it would be superfluous, and because severe constitutional reactions to vaccination would be expected in these hypersensitive individuals. No severe reactions were encountered when this program was followed. Of the procedures used to predict hypersensitivity before vaccination, the skin test was more reliable than the determination of serum agglutinins. Maximal agglutinin titers were attained from 3 to 6 weeks after initial immunization with each of two vaccines prepared by different methods. Comparison of the two vaccines showed no superiority of either on the basis of agglutinin response or hypersensitivity reactions. Skin sensitivity induced by vaccination persisted for two months in only 20 per cent and for six to nine months in only 4 persons. Agglutinins for Brucella developed following injection of Bacterium tularense vaccine in 48 of 207 persons whose initial serum titer was less than 1:10. Twenty-two of 72 vaccinated individuals who worked with highly virulent B. tularense daily over long periods of time acquired primary tularemia infections, an incidence of 30.6 per cent or approximately one–third of the expected incidence for unvaccinated personnel under similar conditions of exposure. Seventy-eight per cent of the infections were either considerably modified or subclinical, a finding which suggests that partial protection was conferred by vaccination. Experience with vaccination against tularemia indicates that it is accompanied by no more hazard than would be anticipated from the use of typhoid vaccine, provided precautions are taken to eliminate hypersensitive individuals by means of a skin test and clinical history. The data presented suggest that prophylactic vaccination should be carried out in individuals exposed to tularemia as an occupational or recreational hazard.