Increase in Directors' Shareholdings

    Increase in Directors' shareholdings

Cambridge, UK - 19 December 2003 - Acambis plc ("Acambis") (LSE: ACM, NASDAQ:
ACAM) announces transactions involving Directors' shareholdings in Acambis.

On 19 December 2003, Gordon Cameron, Chief Financial Officer, exercised options
over a total of 320,954 shares, 170,954 at 170p per share and 150,000 at 92p
per share. At the same time, he sold 259,295 of these shares at 288p per share
in part to fund the cost of exercising the options and the tax liabilities
arising thereon. Following these transactions, Mr Cameron's shareholding in
Acambis increased from 163,849 to 225,508 shares representing approximately
0.21% of Acambis' issued ordinary share capital, of which 133,711 shares are
held by the Trustees of Acambis Employees' Trust on behalf of Mr Cameron.

Also on 19 December 2003, Nicolas Higgins, Chief Business Officer, exercised
options over 150,000 shares at 92p per share. At the same time, he sold 98,100
of these shares at 288p per share in order to fund the cost of exercising the
options and the tax liabilities arising thereon. After these transactions, the
shareholdings in Acambis held by Mr Higgins and his wife had increased from
176,901 to 228,801 shares, representing approximately 0.22% of Acambis' issued
ordinary share capital.

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Enquiries:

Acambis plc                                                                    
                                                                               
Elizabeth Brown, Company Secretary       Tel: [phone]             
                                                                               
Lyndsay Wright, Director of                                                    
Communications                                                                 
                                                                               

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 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.



END