Grain boundaries (GBs) are key players in the plasticity, damage, and failure of polycrystalline materials. A quantitative description of GB-mediated processes, such as migration, sliding, and defect interactions, is hence vital for optimizing the properties of the polycrystal through mechanical processing and has been the subject of long-standing interest. Conventional understanding is that point defects, including vacancies, interstitials, and substitutional atoms, have a drag effect, thereby hindering GB migration. In this work, using atomistic simulations, we reveal that vacancies serve as energetically favorable sites for the nucleation of GB disconnections, thereby inducing shear-coupled migration of certain GBs. Fully 3D nudged elastic band-based calculations demonstrate that vacancies weaken the line tension of a disconnection loop, and hence enhance GB migration.