Acambis PLC Welcomes US Department of Defense’s Transition to ACAM2000(TM) as Its Only Smallpox Vaccine

Cambridge, UK and Cambridge, Massachusetts – 14 February 2008 – Acambis plc (Acambis) (LSE: ACM) welcomes a US Department of Defense announcement that it is now transitioning over to Acambis’ ACAM2000™ as its only smallpox vaccine.

Since 2002, the Department of Defense has used Dryvax®( 1) for its smallpox vaccinations. Dryvax® was produced on calf lymph tissue and has not been manufactured since 1982. ACAM2000™ was developed by Acambis under a contract with the US Centers for Disease Control and Prevention (CDC) to provide the US Government with a modern smallpox vaccine derived from Dryvax®. ACAM2000™ is produced using modern cell-culture manufacturing methods.

Doses of ACAM2000™ are being supplied to the Department of Defense by the CDC through the Strategic National Stockpile. The Department of Defense routinely vaccinates military, emergency-essential and equivalent civilian employees assigned to US Central Command or the Korean Peninsula for more than 15 days. Dryvax® will continue to be used until 29 February, after which ACAM2000™ will be the sole vaccine in use.

In a news release issued by the Department of Defense, Army Colonel Randall Anderson, Director of its Military Vaccine (MILVAX) Agency, said: “The military needs the smallpox vaccine to inoculate troops against biological weapons that may contain the virus. Acambis will provide a long-term, stable supply of the vaccine manufactured within the United States.”

Ian Garland, Chief Executive Officer of Acambis, said: “ACAM2000™ is the result of many years’ work between Acambis and the CDC to provide the US with a new smallpox vaccine developed and manufactured to today’s rigorous standards. We are delighted to see the Department of Defense relying on ACAM2000™. This is in line with our ongoing discussions to secure ACAM2000™ production for the US for the long term and we are proceeding in line with the process to contract award that we outlined previously.”

(1) Dryvax® is a registered trademark of Wyeth Pharmaceuticals Inc. Enquiries: Acambis plc Ian Garland, Chief Executive Officer

Elizabeth Jones, Chief Financial Officer Lyndsay Wright, VP, Communications and IR Tel: +44 (0) 1223 275 300 Brunswick Jon Coles / Justine McIlroy / Annabel Entress Tel: +44 (0) 20 7404 5959

About Acambis Acambis is a leading vaccine company developing novel vaccines that address significant unmet medical needs or substantially improve standards of care. ChimeriVax™-JE, Acambis’ most advanced product in its development-stage pipeline, has to date shown an excellent safety and efficacy profile following pivotal Phase 3 trials. It is currently undergoing paediatric trials in India and is partnered with Sanofi Pasteur and Bharat Biotech. Acambis’ proprietary ChimeriVax™ technology, developed in association with St Louis University, has also been used to develop ChimeriVax™-West Nile, which is undergoing Phase 2 clinical testing, making it the most advanced investigational vaccine against the West Nile virus. Acambis has established a global collaboration with Sanofi Pasteur for further development and commercialisation of the vaccine. ChimeriVax™ has also been applied to development of Sanofi Pasteur’s tetravalent dengue vaccine, which has successfully demonstrated proof-of-concept in a Phase 2 trial by generating 100% seroconversion to all four dengue virus serotypes.

Acambis also has the only vaccine in development against Clostridium difficile bacteria, a leading cause of hospital-acquired infections. C. difficile is estimated to cause at least 360,000 cases of C. difficile-associated disease in the US alone with annual costs to the healthcare system of $3.2bn. Acambis’ influenza programme aims to develop a universal vaccine against influenza, for which a universal ‘A’ strain vaccine, ACAM-FLU-A™ has recently been successfully tested in a Phase 1 trial and H5N1 challenge model. Various further vaccine candidates are in the research and pre-clinical stages.

Acambis is recognised internationally as the leading producer of smallpox vaccines for emergency-use stockpiles held by the US Government and several other governments around the world. Acambis developed its ACAM2000™ smallpox vaccine under contracts with the US Government.

Acambis is based in Cambridge, UK and Cambridge, Massachusetts, US, and is listed on the London Stock Exchange (ACM). More information is available at www.acambis.com.

“Safe Harbour” statement Statements contained within this news release may contain forward-looking comments, which involve risks and uncertainties that may cause actual results to vary from those contained in the forward-looking statements. In some cases, you can identify such forward-looking statements by terminology such as ‘may’, ‘will’, ‘could’, ‘forecasts’, ‘expects’, ‘plans’, ‘anticipates’, ‘believes’, ‘estimates’, ‘predicts’, ‘potential’, or ‘continue’. Predictions and forward-looking references in this news release are subject to the satisfactory progress of research which is, by its very nature, unpredictable. Forward projections reflect management’s best estimates based on information available at the time of issue.

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