Study describes advantages of Acambis' clonal smallpox vaccine

Cambridge, UK and Cambridge, Massachusetts - 19 August 2003 - A new smallpox
vaccine developed by Acambis (LSE: ACM, NASDAQ: ACAM) is made in modern cell
culture system, is free from contaminating bacteria and viruses, and could be
less neurovirulent than a first-generation vaccine while providing equivalent
immunogenicity, according to pre-clinical data published in Nature Medicine.

Acambis' vaccine was developed in response to the US Government's requirement
for a stockpile of smallpox vaccine for use in the event of an outbreak,
including the potential of smallpox being used as a bioterrorist weapon.

Old, "first-generation" smallpox vaccines were grown in the skin of calves or
other large animals. As such a production method is considered unacceptable
today, Acambis aimed to develop a vaccine that was suitable for modern
manufacture in cell culture and that matched or exceeded first-generation in
immunogenicity but did not exceed it in virulence markers that might indicate
reactogenicity in humans.

Acambis derived its new vaccine from Dryvax�, a first-generation vaccine
registered in the US and used during the worldwide smallpox eradication
program. In the initial phase of this work, Acambis discovered that the
first-generation vaccine contained multiple subpopulations of virus, including
variants that were highly virulent in pre-clinical models. As this observation
fitted with previous research (see notes 1, 2), it was not considered
acceptable to generate the new vaccine simply by inoculation of the
first-generation product into cell culture. Consequently, Acambis prepared a
number of viral clones from which one could be chosen that closely resembled
the first-generation vaccine's profile but had an acceptable or improved safety
profile. Use of a clone also removed possible adventitious viral contaminants
and ensured consistency of manufacture. Through a series of pre-clinical tests,
Acambis selected a preferred vaccine candidate that was consistently less
virulent and provided equivalent protection.

A randomized, double-blind clinical study was carried out under an
Investigational New Drug Application approved by the US Food and Drug
Administration to evaluate the safety, tolerability and immunogenicity of
Acambis' vaccine and Dryvax in 60 healthy adults aged 18 to 29 who had not
previously been vaccinated against smallpox. The trial reinforced the findings
of the pre-clinical tests, with the two vaccines having equivalent protection
profiles and no serious adverse events being recorded.

Dr Thomas Monath, Acambis' Chief Scientific Officer, commented:

"The development of a clonal vaccine that can be manufactured using modern
cell-culture methods indicates that Acambis' new smallpox vaccine represents an
advance over the first-generation vaccine in terms of purity, quality, freedom
from bacterial contamination allowed in the old vaccine and the absence of
bovine adventitious agents. While we can not prove, without large-scale human
experience, that our vaccine is safer for humans with respect to a lower
incidence of postvaccinal encephalitis, this remains a possibility based on the
pre-clinical data."

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Notes:

1. Kutinova, L. et al. Search for optimal parent for recombinant vaccinia virus
vaccines. Study of three vaccinia virus vaccinal strains and several virus
lines derived from them. Vaccine 13, 487- 493 (1995).

2. Kutinova, L. et al. Influence of the parental virus strain on the virulence
and immunogenicity of recombinant vaccinia viruses expressing HBV pre-S2-S
protein or VZV glycoprotein l. Vaccine 14, 1045-1052 (1996).

Enquiries:

Acambis                                                                        
                                                                               
Dr Thomas Monath, Chief Scientific       Tel: +1 (617) 761 4200                
Officer                                                                        
                                                                               
Lyndsay Wright, Director of              Tel: +44 (0) 1223 275 300             
Communications                                                                 
                                                                               

Notes to editors:

Digital online identifier: 10.1038/Nm916
To access this paper online, visit http://dx.doi.org/10.1038/Nm916

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 provides governments around the world with the full portfolio
of related smallpox vaccine products required to protect their citizens against
the threat of smallpox virus being used as a bioterrorist weapon. It is
supplying 209 million doses of smallpox vaccine to the US Government as part of
its plan to have a dose for every man, woman and child for use in the event of
a smallpox outbreak.

Acambis is establishing a travel vaccines franchise, including vaccines against
yellow fever, Japanese encephalitis, dengue fever and typhoid. Acambis also has
the most advanced vaccine in development targeting the West Nile virus, which
has spread to 44 US States in the last three 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.

Acambis' smallpox vaccine
Acambis' new smallpox vaccine is based on the same vaccinia virus strain, the
New York City Board of Health strain, that was licensed in the US and used for
routine immunization against smallpox prior to the global eradication of
smallpox in the 1970s. Compared with the previously licensed, first-generation
vaccine, Dryvax�, improvements have been made both in the development of this
vaccine and the methods by which it is manufactured. Dryvax� is a registered
trademark of Wyeth.

Smallpox vaccination
Vaccinia (cowpox) vaccines have been used to control smallpox for more than 200
years, ever since Dr Edward Jenner's first experiments in 1796. Immunity
develops rapidly following vaccination, generally being protective even in
people already exposed to smallpox and incubating the virus but not yet
clinically ill. Vaccinia is delivered by pricking the skin with a special
(bifurcated) needle.

"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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