Thymalfasin (thymosin-α1, Zadaxin) is a 28-amino acid synthetic peptide that is identical to the natural thymosin-α1 produced by the thymus gland [290]. It possesses immunoregulatory properties owing primarily to its ability to activate various immune cells, particularly T cells. It is used alone or in combination with INFs as an immunomodulator for the treatment of chronic HBV and HCV infections [291,292]. Thymalfasin can also be used for the treatment of chemotherapy-induced immune suppression, and to increase the efficacy of HBV and influenza virus vaccines [293]. Currently, it is being tested in few clinical trials in the context of COVID-19. An important study is the trial to prevent COVID-19 infection in elderly renal dialysis patients (NCT04428008; n = 240).