 Subjects will be personnel from 2 intramural campuses of the National Institute of Allergy and Infectious Diseases who may be exposed accidentally to any strain or serotype of viable TBEV. Approximately 160 individuals are eligible to participate. Inclusion and exclusion criteria are defined. The rapid immunization schedule injections on Days 0, 14, and 161 will be used and subjects will have labs drawn 21 days after the 2nd, 3rd and 4th vaccine injections to determine seroconversion. Subjects who seroconvert to TBEV will be offered a booster dose of the vaccine 3 years from the date of receipt of the third dose of the vaccine. Subjects who are seropositive at entry into the study will be offered a booster dose of the vaccine every 3 years from Day 0. 