Acambis PLC Concludes C. difficile Vaccine Formulation Work on Schedule and Will Commence Proof-of-Concept trial in 2008

Cambridge, UK and Cambridge, Massachusetts – 18 December 2007 – Acambis plc (Acambis) (LSE: ACM), a leading vaccine development company, announces an update on its programme to develop the world's first vaccine against Clostridium difficile-associated disease (CDAD). C. difficile infection is the most common cause of hospital-acquired diarrhoea in the developed world, resulting in at least 360,000 cases of disease in the US alone, with estimated annual costs to the US and European healthcare systems totalling more than $5bn(1,2).