The present disclosure provides a method of treating a disease associated with a respiratory virus. The method comprises administering an effective amount of a pharmaceutical composition prepared by removing albumin from a solution of a human serum albumin composition and/or comprising a diketopiperazine with amino acid side chains of aspartic acid and alanine (DA-DKP), such as a low molecular weight fraction of human serum albumin. The present disclosure also provides a pharmaceutical product as well as a kit comprising DA-DKP.