 This is an open label trial of a non-US licensed vaccine for tick-borne encephalitis. The vaccine has been licensed by Baxter, now following an acquisition by Pfizer Inc in Vienna, Austria since 2001, and has an extensive safety record in multiple European countries. Field effectiveness studies suggest 99 percent protection against disease transmitted by the natural routes of either tick bite or ingestion of contaminated, unpasteurized milk. The vaccine is also considered to be effective against laboratory exposures and is used routinely for this purpose in European laboratories. The US Centers for Disease Control and Prevention and the National Institutes of Health acknowledge the effectiveness of the vaccine by allowing those who have received it to study tick-borne encephalitis virus TBEV in isolation facilities rated at BSL-3 rather than the more stringent BSL-4, with the exception of the Russian Spring-Summer Encephalitis strain. 