A nanosystem and methods of treating, including prophylactically, coronavirus infections, such as those caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), by administering such nanosystem to a patient is presented. The nanosystem may be comprised of a single or a combination of therapeutic agents, optionally encapsulated in a nanoparticle having a targeting moiety directed to the particular coronavirus. For CoV-2 infections, at least one therapeutic agent, such as the dual DPP4/ACE2 inhibitor sitagliptin, may optionally be encapsulated within a nanoparticle having a fatty acid such as linoleic acid, as the targeting moiety. Administration can occur intranasally prior to infection for prophylactic treatment or post-infection for treatment of the viral infection.