Interferons (IFNs) mediate cellular defence against viral pathogens by upregulation of interferon-stimulated genes (ISGs) whose products interact with viral components or alter cellular physiology to suppress viral replication (1-3). Among the ISGs that can inhibit influenza A virus (IAV) (4) are the myxovirus resistance 1 (MX1) GTPase (5) and IFN-induced transmembrane protein 3 (IFITM3) (6, 7). Here we use ectopic expression and gene knock-out to demonstrate that the IFN-inducible 219 amino acid short isoform of human nuclear receptor coactivator 7 (NCOA7) is an inhibitor of IAV as well as other viruses that enter the cell by endocytosis, including hepatitis C virus (HCV). NCOA7 interacts with the vacuolar H+-ATPase (V-ATPase) and its expression promotes cytoplasmic vesicle acidification, lysosomal protease activity and the degradation of endocytosed antigen. Step-wise dissection of the IAV entry pathway demonstrates that NCOA7 inhibits fusion of the viral and endosomal membranes and subsequent nuclear translocation of viral ribonucleoproteins (vRNPs). NCOA7, therefore, provides a mechanism for immune regulation of endo-lysosomal physiology that not only suppresses viral entry into the cytosol from this compartment but may also regulate other V-ATPase-associated cellular processes such as physiological adjustments to nutritional status, or the maturation and function of antigen presenting cells.