Vanadium dioxide undergoes an unusual insulator-metal transition (IMT), and after decades of study, the origin of the IMT remains hotly debated. Here, by analyzing spectral-weight transfers (SWTs) of x-ray absorption spectroscopy at the and O K edges on specially designed films, we observe band splitting at the edges across the IMT, accompanied by anomalous SWTs as high as at the edge, indicating strong electronic correlations. Surprisingly, a few oxygen vacancies induce dramatic SWTs at the edge, but the sample remains conducting. Supported by theoretical calculations, we find that in the metallic state, direct and hybridized orbital correlations are screened by hybridized orbitals, while in the insulating state they are strongly correlated due to changes in the oxygen orbital occupancy. Our result shows the importance of screenings and electronic correlations for IMTs in .