Smallpox vaccine and trading update

Cambridge, UK and Cambridge, Massachusetts - 15 January 2004 - Acambis plc
("Acambis") (LSE: ACM, NASDAQ: ACAM) announces an update on its smallpox
vaccine programme.

At the time of its third quarter results announcement in November 2003, Acambis
provided an update on the contract with the US Government to supply quantities
of the ACAM2000 investigational smallpox vaccine for its emergency-use
Strategic National Stockpile. Acambis indicated that the remaining doses of the
investigational vaccine to be delivered under the 155 million-dose order with
the US Centers for Disease Control and Prevention ("CDC") and approximately 18
million of the additional doses ordered by the CDC were expected to be
delivered during the fourth quarter of 2003.

A large delivery of vaccine was scheduled to take place during the last week of
December 2003. Shortly before the delivery was due to occur, Acambis was
informed by the CDC that the US Government was concerned about the movement of
vaccine during a period of heightened security alert. As a result, CDC said it
would be unable to take delivery of the shipment of vaccine on the scheduled
date. With the US national security threat level now having been lowered, a
revised shipment date of early February to deliver these remaining vaccine
doses has been scheduled with the CDC.

As a result, unaudited pre-tax profits for the year ended 31 December 2003 are
estimated to be �12m lower as compared to previous guidance. Consequently,
pre-tax profits for the year ended 31 December 2004 are expected to be around �
12m higher as compared to previous guidance. Acambis will provide a fuller
update to 2004 guidance when it announces its preliminary results for the year
ended 31 December 2003 on Tuesday, 2 March 2003.

Unaudited cash and short-term investments at 31 December 2003 were slightly
higher than previously anticipated at around �125m.

Acambis is continuing its programme to evaluate the safety and efficacy of its
ACAM2000 smallpox vaccine. In December, it initiated Phase III trials to
evaluate the safety and efficacy of ACAM2000 in comparison with a previously
licensed vaccine, Dryvax�. The two Phase III trials will include people who
have previously been vaccinated against smallpox and those who are na�ve to
smallpox vaccination.

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Enquiries:

Acambis plc

Gordon Cameron, Acting Chief Executive Officer and Chief Financial Officer:
Tel: +1 (617) 761 4200

Lyndsay Wright, Director of Communications: Tel: +44 (0) 1223 275 300

Financial Dynamics

David Yates/ Charlie Armitstead: Tel: +44 (0) 20 7831 3113

About Acambis

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. A licence application has been submitted to the US Food and Drug
Administration for a vaccine against yellow fever and clinical trials are being
conducted for vaccines against Japanese encephalitis, travellers' diarrhoea 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 2002 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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