IFNA1 and hepatitis A virus infection: The most important studies on IFN α for HDV treatment are two randomized controlled trials, Hep-Net–International Delta Hepatitis Intervention Trial (HIDIT I) HIDT I and Hep-Net–International Delta Hepatitis Intervention Trial II (HIDT II) (Wedemeyer et al., 2011; Wedemeyer et al., 2019b) and many uncontrolled trials with prospective and retrospective designs.