As early as possible before you travel — ideally six or more weeks before departure. This allows time for at least two doses with the standard one-month gap, giving you the best immune response before you arrive. Tick season runs broadly from April to November, with peak activity in spring and early autumn, so if you’re planning a summer trip to Central Europe, starting the course in late winter or early spring makes sense. If you’ve left it later, the accelerated two-week schedule is available.