Antitoxin component of a type II toxin-antitoxin (TA) system. Upon expression in E.coli neutralizes the effect of toxin VapC1. In vitro inhibits the RNase activity of VapC1. Forms multimers, as well forming as a complex with VapC1. More highly expressed in early growth phase, expression decreases as cell density decreases. Part of the vapB1-vapC1 operon. Belongs to the VapB family.