$425m, ten-year ACAM2000â„¢ smallpox vaccine contract awarded to

$425m, ten-year ACAM2000â„¢ smallpox vaccine contract awarded to
Acambis by US Government

Cambridge, UK and Cambridge, Massachusetts – 23 April 2008 – Acambis plc (Acambis)
(LSE: ACM) announces that it has been awarded a $425m (c. £212m), ten-year contract by the
US Government agency, the Centers for Disease Control and Prevention (CDC), to provide it with
a warm-base manufacturing capability for Acambis’ ACAM2000™ smallpox vaccine. Warm-base
manufacturing entails the maintenance of an ongoing production readiness capability through
annual production runs.

Under the terms of the contract, Acambis will:

• Establish a US-based manufacturing capability for ACAM2000™;
• Deliver against CDC orders for a minimum of nine million doses per annum for the eight
years from year three to year ten of the contract; and
• Undertake activities to maintain its product licence.
Acambis developed ACAM2000â„¢ under a contract with the CDC and has already delivered more
than 195 million doses of this vaccine to the CDC for the US’s Strategic National Stockpile. Doses
are also being supplied by the CDC to the Department of Defense, which has transitioned over to
ACAM2000â„¢ for routine vaccination of military, emergency-essential and equivalent civilian
employees.

Acambis will establish a US-based manufacturing capability by transferring the ACAM2000â„¢
production process to Acambis’ facilities in Canton, MA and Rockville, MD. Previously, elements
of the process were conducted outside the US or by third-party contractors.
The CDC will procure at least nine million doses of ACAM2000â„¢ a year in contract years three to
ten. The structure of the contract allows the CDC to purchase up to 39 million doses in contract
years five to ten, should the need arise. This would increase the headline value of the contract to
around $660m. For the dose-delivery activities, Acambis will receive payment on a fixed-price
basis.

In addition, Acambis will undertake licence maintenance activities throughout the life of the
contract on a cost-plus-fixed-fee basis. In the initial years, this includes conducting a Phase 4
study in US military personnel, establishing an enhanced surveillance programme and
myocarditis registry to monitor the safety profile of the vaccine, and undertaking a bridging trial to
support a licence amendment for transfer of bulk production to its Canton, MA facility.
Of the $425m (c. £212m) revenues, approximately two-thirds relates to the delivery of doses in
contract years three to ten, and one-third to licence maintenance activities.

Ian Garland, Chief Executive Officer of Acambis, said:
“We are delighted to be awarded this contract by the CDC, which marks the achievement of one
of Acambis’ major corporate goals. It is highly satisfying to know that, following eight years’
collaboration with the CDC to develop ACAM2000â„¢, this core part of the US Government's
defence against smallpox has been secured by Acambis for the long term.”

-ends-
A meeting and conference call for analysts will be held today at 9.30 a.m. BST. For details, contact Annabel
Entress at Brunswick on telephone number +44 (0) 20 7404 5959. An instant replay of the call will be
available until 30 April 2008 on telephone number UK: +44 (0) 20 8196 1998 and US: + 1 (866) 583 1035.
The pin code is 949716#. A webcast of the call will also be available via Acambis’ website at
www.acambis.com. The webcast replay will be available for 12 months until 23 April 2009.

Enquiries:
Page 2 of 2
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 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 the endemic region and is partnered with Sanofi
Pasteur. Acambis’ proprietary ChimeriVax™ technology, developed in association with St Louis University,
has also been used to develop ChimeriVaxâ„¢-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’ ACAM-CDIFF™ vaccine is believed to be 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, and annual costs to US and European
healthcare systems are estimated to be in excess of $7bn a year. Acambis’ influenza programme aims to
develop a universal vaccine against influenza, for which a universal ‘A’ strain vaccine, ACAM-FLU-A™, was
recently tested in a Phase 1 trial and pre-clinical challenge study. Acambis is currently undertaking preclinical
testing of a vaccine candidate, dl5-29, against genital herpes.

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 ACAM2000â„¢ 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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