Acambis becomes first company to enter Phase II testing of vaccine against West Nile virus Cambridge, UK and Cambridge, Massachusetts - 20 December 2005 - Acambis plc (“Acambis”) (LSE: ACM, NASDAQ: ACAM) announces that it has started a Phase II clinical trial of its investigational vaccine against the West Nile virus, ChimeriVax™-West Nile, in healthy adult subjects. Acambis is the first company to enter a Phase II trial of a West Nile vaccine.