Immunization against Tularemia: Analysis of the Effectiveness of Live Francisella tularensis Vaccine in Prevention of Laboratory-Acquired Tularemia

Abstract

A retrospective analysis was made of cases of laboratory-acquired infections with Francisella tularensis among civilian employees at Fort Detrick, Maryland. The incidence and clinical presentation of tularemia during the decade 1950–1959, when the phenol-killed Foshay vaccine was used routinely for immunization of employees, were compared with similar data from the first decade (1960–1969) after the live tularemia vaccine had come into use. The incidence of typhoidal tularemia fell (from 5.70 to 0.27 cases per 1,000 at-risk employee-years; P < 0.001), whereas the incidence of ulceroglandular tularemia remained unchanged (from 0.76 to 0.54 cases per 1,000 at-risk employee-years). Ulceroglandular tularemia in employees immunized with live vaccine was characterized by clinical signs and symptoms that were milder than those in employees vaccinated with the Foshay vaccine.