Acambis commences first human clinical trial of West Nile vaccine

Cambridge, UK and Cambridge, MA - 6 November 2003 - Acambis (LSE: ACM, NASDAQ:
ACAM), a leading developer of vaccines against infectious diseases, announces
the start of a Phase I trial of its investigational vaccine against West Nile
virus, ChimeriVax-West Nile.

Since it was first identified in New York in 1999, the West Nile virus has
swept through 45 US states, causing disease in more than 12,000 people and
resulting in the deaths of several hundred individuals. In 2003 alone, it has
affected more than 8,200 people and caused 182 deaths. The virus has also
spread south to Central America and the Caribbean, and north into Canada where
it has been identified in seven provinces.

Acambis used its proprietary ChimeriVaxTM technology to develop the
investigational ChimeriVax-West Nile vaccine and has conducted a series of
successful pre-clinical studies on the vaccine. Acambis has now started a Phase
I clinical trial in humans.

The trial is being conducted in Lenexa, Kansas under a US Food and Drug
Administration Investigational New Drug application. The trial is a randomised,
double-blind out-patient study in 60 healthy adult volunteers. It will test the
safety, tolerability and immunogenicity of the ChimeriVax-West Nile vaccine.

 

The 60 volunteers will receive either a single vaccination with one of the
three different dose levels of ChimeriVax-West Nile being tested or a licensed
yellow fever vaccine that is being used as a control in the trial. Safety and
tolerability will be judged by recording adverse reactions to the vaccine and
immunogenicity will be measured in terms of antibody levels and T cell
responses generated against West Nile virus.

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

"West Nile virus has become established as an endemic and epidemic disease that
poses a significant threat to human health and a preventive vaccine could
become a major factor in the fight against this virus. Acambis began work on
this project within months of the virus being diagnosed in the US and we are
pleased to be the first company to start human clinical trials to evaluate a
vaccine against West Nile."

Acambis' work on ChimeriVax-West Nile has been partly financed by a $3 million
grant from the US National Institutes of Health, awarded to Acambis in August
2000.

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Enquiries:

Dr John Brown, Chief Executive Officer

Lyndsay Wright, Director of Communications

Tel: +44 (0) 1223 275 300

Gordon Cameron, President of Acambis Inc. and Chief Financial Officer

Thomas Monath, Chief Scientific Officer

Tel: +1 (617) 761 4200

Notes to editors:

Acambis plc

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 that 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 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. More information on Acambis' West Nile project
can be found at www.acambis.com/westnile.

ChimeriVaxTM

ChimeriVax is a proprietary technology that Acambis is using in the development
of a number of potential vaccines. Currently, Acambis is conducting clinical
trials on three vaccines developed using this technology: ChimeriVax-JE against
Japanese encephalitis; ChimeriVax-Dengue against dengue fever; and
ChimeriVax-West Nile against the West Nile virus.

West Nile virus

West Nile virus was first identified in 1937 in the West Nile district of
Uganda from which it takes its name. Since then, it has been seen in Africa,
Europe, the Middle East, west and central Asia, Oceania and, most recently,
North America. Recent human outbreaks have occurred in Algeria (1994), Romania
(1996/7), Czech Republic (1997), the Democratic Republic of Congo (1998),
Russia (1999), US (1999-2002) and Israel (2000).

West Nile was first detected in New York in the summer of 1999. That year, the
city experienced 62 cases of West Nile infection and seven people died.
Although human cases of West Nile were found only in New York City during 1999,
the virus was detected in animals and birds in the states of Connecticut, New
Jersey, New York and Maryland. By the end of 2000, the virus had been found in
a further nine states taking the total number of infected states to 13. That
year, the virus caused severe infections in 18 people and for two of them it
was fatal. During 2001, the virus spread through another 16 states, killing
nine and causing severe illness in 66.

This year, the virus has had a greater impact than in any of the previous
years. It has spread to a total of 45 US states, and there have been more than
7,700 human infections and 166 deaths.

"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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