Antitoxin component of a type II toxin-antitoxin (TA) system (PubMed:25391136, PubMed:27672196). Neutralizes the effect of cognate toxin VapC1 (PubMed:25391136, PubMed:27672196) but not non-cognate toxin VapC2 (PubMed:27672196). Forms a complex with VapC1, and a weak complex with VapC2 (PubMed:27672196). More highly expressed in early growth phase, expression decreases as cell density decreases. Part of the vapB1-vapC1 operon. Belongs to the VapB family.