As the investigators wish to investigate the ability of the vaccine to specifically prime subjects in a targeted way, participants must be naive to the vaccine antigens and so must not have had the vaccine or TBEV infection before. Therefore the investigators will use TicoVac - a TBEV vaccine licenced in the UK that UK adults have not generally received, as TBEV infection is not endemic in the UK. TicoVac is widely used in central and eastern Europe where TBEV is endemic but extremely uncommon, and is offered to travellers from UK to endemic areas who are likely to engage in high risk activity (hiking, trekking).