 Open Orphan PLC AIM:ORPH, OTC:OPORF has highlighted positive results of a human challenge study assessing Enanta Pharmaceuticals NASDAQ:ENTA respiratory syncytial virus RSV antiviral candidate, EDP-938, which is being advanced by Enanta Pharmaceuticals Inc. AIM-quoted Open Orphan, which is a contract research organisation CRO specialising in the testing of infectious and respiratory disease products, helped facilitate the challenge trial which enrolled 178 healthy adult volunteers in an age range between 18 and 55. 