In this paper, a seismically isolated (SI) bridge is investigated by employing supplemental vibration control systems (VCS) to enhance its dynamic performance. The main objective of the proposed seismic protection strategy is to reduce the shear deformation of the bearings, while at the same time, retaining the shear abutment force in reasonable ranges, as compared to the initial SI bridge structure. The examined bridge structure is a two-span bridge, with bearings in the abutments, and pier. The proposed VCS are based on the KDamper concept and are implemented parallel to the bearings. The KDamper is essentially an extension of the conventional Tuned Mass Damper (TMD), by properly introducing a negative stiffness (NS) element to the additional mass of the TMD, artificially amplifying its inertia force. This way, a significantly lower added mass is required, thus enabling enhanced performance without heavy parasitic masses. A comparative assessment is performed by installing a highly mass TMD, and a TMD with an inertance element (TMDI system). The excitation input in the design process of the KDamper-based VCS, the TMD, and the TMDI is a set of artificial accelerograms that match the EC8 acceleration design spectrum. The dynamic response of the SI bridge supplemented with the examined VCS is assessed with real earthquake records. Based on the numerical results obtained, the KDamper-based VCS outperforms the controlled structure with a TMD having 50 times higher additional mass, and a TMDI with 10 times higher mass and an inertance ratio up to 30%.