Hepatitis Delta Virus (HDV) is a co-infection that affects 5-6% of HBV patients. Compared to HBV infection alone, HDV co-infected patients are at risk of 2-3x faster onset of both cirrhosis and hepatocellular carcinoma. While there are an estimated 15-20 million HBV/HDV-infected patients worldwide, HDV is classified as an orphan disease in both the U.S. and EU.

The active metabolite of ATI-2173 significantly decreased HDV RNA levels in woodchuck models of HBV/HDV. Conversely, neither tenofovir nor entecavir have shown activity against HDV in animal models or human studies.