Acambis collaborates with WHO on Japanese encephalitis vaccine

Cambridge, UK and Cambridge, Massachusetts - 25 November 2003 - Acambis plc
("Acambis") (LSE: ACM, NASDAQ: ACAM) announces that it is to collaborate with
the World Health Organization ("WHO") on the development of Acambis'
investigational vaccine ChimeriVax-JE against Japanese encephalitis ("JE").

Under a Memorandum of Understanding between WHO and Acambis, WHO will provide
assistance and funding for paediatric trials of ChimeriVax-JE in endemic
countries. This is part of WHO's efforts to enable the development of effective
paediatric vaccines against JE for developing countries where the virus is
endemic.

In the first instance, WHO will assist with a trial of ChimeriVax-JE, which
Acambis plans to conduct at Mahidol University in Thailand. The trial will
investigate the safety, tolerability and immunogenicity of ChimeriVax-JE in age
groups stepping down to the target population of infants in their second year
of life, in accordance with current paediatric schedule vaccination in that
country. WHO will provide technical advice, infrastructure and monitoring
services, and also financial support.

Acambis' ChimeriVax-JE vaccine has already been tested in two Phase II clinical
trials and is currently undergoing a separate two-year study in Australia to
expand safety and efficacy information and to investigate duration of immunity.

JE is a mosquito-borne virus that occurs throughout China, Korea, the Indian
sub-continent, south-east Asia and parts of Melanesia and Australia. It is
considered to be the world's most significant cause of viral encephalitis. Up
to 30% of affected people die of the disease caused by the virus and many
survivors have permanent neurological disabilities. Approximately 35,000 human
cases of JE are reported annually, but it is thought that the true incidence
could be in excess of 50,000 as surveillance and reporting rates are poor.
Three billion people live in JE-endemic regions and more than 70 million
children are born each year in endemic countries.

Dr John Brown, Chief Executive Officer of Acambis, commented:

"Access to endemic countries is a key part of our vaccine development strategy.
We are delighted to be working with WHO in the development of our ChimeriVax-JE
vaccine and believe the considerable expertise they have in conducting trials
in endemic countries will be invaluable."

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Enquiries:

Acambis plc                                                         
                                                                    
Dr John Brown, Chief Executive Officer     Tel: +44 (0) 1223 275 300
                                                                    
Lyndsay Wright, Director of Communications                          
                                                                    
Gordon Cameron, Chief Financial Officer    Tel: +1 (617) 761 4200   
                                                                    
Financial Dynamics                                                  
                                                                    
David Yates/Charlie Armitstead             Tel: +44 (0) 20 7831 3113
                                                                    

Notes to editors:

Acambis is a leading developer of vaccines to prevent and treat infectious
diseases.  Recognised internationally as the leading producer of smallpox
vaccines, Acambis is developing a second-generation smallpox vaccine which is
currently undergoing clinical trials and, under a unique arrangement given the
threat of smallpox being used as a bioterrorist weapon, is manufacturing
emergency-use stockpiles of this investigational vaccine for the US Government
and other governments around the world. Acambis is establishing a travel
vaccines franchise through its US-based subsidiary Berna Products Corporation,
which markets Vivotif�, the world's only oral typhoid vaccine, in North
America. Acambis has a number of other potential travel vaccines in development
and is conducting clinical trials of vaccines against yellow fever, Japanese
encephalitis and dengue fever. Acambis recently became the first company to
start human clinical trials of a vaccine targeting the West Nile virus, which
has spread to 45 US States in the last four years.

Acambis is based in Cambridge, UK and Cambridge, Massachusetts, US. Its primary
listing is on the London Stock Exchange (ACM) and its shares are listed in the
form of American Depositary Receipts on Nasdaq (ACAM). More information is
available at www.acambis.com.

"Safe Harbor" statement under the Private Securities Litigation Reform Act of
1995:

The statements in this news release that are not historical facts are
forward-looking statements that involve risks and uncertainties, including the
timing and results of clinical trials, product development, manufacturing and
commercialisation risks, the risks of satisfying the regulatory approval
process in a timely manner, the need for and the availability of additional
capital. For a discussion of these and other risks and uncertainties see "Risk
factors" in the Company's Annual Report and Form 20-F for the most recently
ended fiscal year, in addition to those detailed in the Company's filings made
with the Securities and Exchange Commission from time to time. These
forward-looking statements are based on estimates and assumptions made by the
management of Acambis and are believed to be reasonable, though are inherently
uncertain and difficult to predict. Actual results or experience could differ
materially from the forward-looking statements.



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