Concomitant administration of an antigen and antibodies of the respective specificity has been shown to result in reduced levels of actively produced antibodies. This has also recently been observed in a clinical trial on simultaneous passive and active immunization against tick-borne encephalitis virus (TBEV). In the current study the influence of simultaneous passive and active immunization on vaccine induced protective immunity against TBEV has been evaluated in a mouse model. Two immunizations with licensed whole-killed TBEV vaccines gave close to complete protection. Administration of human or mouse TBEV antibodies together with the first vaccine dose resulted in a significant reduction of vaccine induced protection against TBEV challenge. This effect was even more pronounced than that observed earlier on the levels of vaccine induced antibody.