Dr. Janssen has led numerous international multicenter clinical and translational studies on the natural history and treatment for chronic viral hepatitis and other liver diseases. His clinical and translational research aiming for immunological control and cure of hepatitis B and C has led to several globally used novel treatment concepts. He is currently the most cited global expert in chronic hepatitis B (Expertscape nr 1 among 28.932 scientists). His research contributions include sustained federal funding (greater than 20 years), over 600 peer reviewed publications, an H-index of 115, and over 60,000 citations (Google Scholar). He has acquired over $50 million USD in research funding from many different organizations among which NIH, European Commission, CIHR, NWO and ZonMW.

He has received several prestigious international awards and has mentored over 50 PhD students, several of whom have taken leadership positions in the field of Hepatology or Virology. In addition to his longstanding expertise in antiviral therapy of chronic viral hepatitis, he is a leading scientist in the field of vascular disorders of the liver.