The present invention addresses the problem of providing a vaccine which as yet has not been provided for the disease HHV-6B, which is the cause of exanthema subitum in infants, and the problem of providing an effective screening method for other therapeutic drugs. The above-mentioned problems are solved by providing an epitope specific to HHV-6B, wherein, of the amino acid sequence (QALCEGGHVFYNP) represented by positions 484 to 496 of SEQ ID NO: 2 or a modified sequence thereof, the epitope either has a sequence comprising at least five consecutive amino acids including at least E, or a sequence that preserves the 487
