Positive Phase I and Pre-Clinical Data Suggest Acambis´ M2e-Based Universal Influenza Vaccine, ACAM-FLU-A(TM), Could Tackle Influenza Pandemics

Acambis plc (Acambis) (LSE:ACM), a leading vaccine development
company, today announced positive data from two trials of its
universal influenza vaccine ACAM-FLU-A(TM). The novel vaccine targets
the M2e peptide, which is found unchanged on the surface of all ´A´
strains of the influenza virus, including all pandemic influenza
strains. As such, this vaccine could overcome the current need to
adapt influenza vaccines every year to correspond to circulating
strains. The Phase 1 clinical trial showed the vaccine to be well
tolerated and immunogenic and the pre-clinical challenge study
suggests that this M2e-based vaccine can protect against highly
pathogenic viruses such as pandemic influenza strains, including H5N1.

Currently, influenza vaccines are regularly reformulated owing to
the rapid mutation of the virus. ACAM-FLU-A(TM) combines the conserved
M2e peptide with a carrier molecule from Hepatitis B, which is used to
help stimulate the immune system. This novel vaccine design means that
ACAM-FLU-A(TM) could potentially provide protection against ´A´
strains of influenza. Historically, influenza pandemics have only been
caused by ´A´ strains of the virus. Therefore ACAM-FLU-A(TM) has
potential both as a vaccine against pandemic influenza and as part of
seasonal influenza vaccination.

The Phase 1 trial was a double-blind, placebo-controlled study
conducted at three centres in the USA. The study consisted of four
arms: placebo, ACAM-FLU-A(TM) alone or combined with aluminium
hydroxide or QS-21. Healthy volunteers aged between 18 and 40 were
given two doses 30 days apart, their immune response against the M2
protein was tested after 60 days and any adverse events to the vaccine
were recorded.

The vaccine was shown to be immunogenic and well-tolerated, with
no serious adverse events. Whilst immune responses were seen in all
the vaccinated groups, blood tests showed that the highest immune
responses occurred in the group who received ACAM-FLU-A(TM) with
QS-21. In this group, 90% of people who received ACAM-FLU-A(TM) plus
QS-21 had antibodies to the M2 protein in their system. QS-21
Stimulon(R) adjuvant is an investigational adjuvant (immune stimulant)
provided under an agreement with Antigenics Inc., which has recently
been converted to a non-exclusive license and supply agreement.

The pre-clinical study tested the ability of an M2e-based vaccine
to protect against the Vietnam 2004 strain(1) of H5N1 avian influenza
(bird flu). The H5N1 virus was lethal in the placebo-treated group,
whereas 70% of those in the group vaccinated with the M2e-based
vaccine from the same influenza strain were protected.

Dr Michael Watson, Executive Vice President, Research &
Development at Acambis commented: "Taken together, the data from these
two trials demonstrate the potential of Acambis´ approach to offer
protection against ´A´ strains of the influenza virus, including
pandemic influenza strains. As a universal vaccine, ACAM-FLU-A(TM) can
potentially overcome many of the drawbacks of existing influenza
vaccines. It can be manufactured at any time of the year, and could be
stockpiled in advance of a pandemic or potentially used routinely to
ensure population protection against future pandemics."

Following these results, Acambis will explore partnering in
parallel with continued development of ACAM-FLU-A(TM).

About Acambis

Acambis is a leading vaccine company developing novel vaccines
that address significant unmet medical needs or substantially improve
standards of care. ChimeriVax(TM)-JE, Acambis´ most advanced product
in its development-stage pipeline, has to date shown an excellent
safety and efficacy profile following pivotal Phase 3 trials. It is
currently undergoing paediatric trials in India and is partnered with
Sanofi Pasteur and Bharat Biotech. Acambis´ proprietary ChimeriVax(TM)
technology, developed in association with St Louis University, has
also been used to develop ChimeriVax(TM)-West Nile, which is
undergoing Phase 2 clinical testing, making it the most advanced
investigational vaccine against the West Nile virus. Acambis has
established a global collaboration with Sanofi Pasteur for further
development and commercialisation of the vaccine. ChimeriVax(TM) has
also been applied to development of Sanofi Pasteur´s tetravalent
dengue vaccine, which has successfully demonstrated proof-of-concept
in a Phase 2 trial by generating 100% seroconversion to all four
dengue virus serotypes.

Acambis also has the only vaccine in development against
Clostridium difficile bacteria, a leading cause of hospital-acquired
infections. C. difficile is estimated to cause at least 360,000 cases
of C. difficile-associated disease in the US alone with annual costs
to the healthcare system of $3.2bn. Acambis´ influenza programme aims
to develop a universal vaccine against influenza, for which a
universal ´A´ strain vaccine, ACAM-FLU-A(TM), has completed a Phase 1
trial. It also includes various further vaccine candidates in the
research and pre-clinical stages.

Acambis is recognised internationally as the leading producer of
smallpox vaccines. Acambis´ ACAM2000(TM) (Smallpox (Vaccinia) Vaccine,
Live) vaccine for active immunisation against smallpox disease for
persons determined to be at high risk for smallpox infection was
licensed by the US Food and Drug Administration in August 2007.
Acambis has manufactured doses of ACAM2000(TM) for emergency-use
stockpiles held by the US Government and several other governments
around the world. For safety and prescribing information, please refer
to www.acambis.com/ACAM2000.

Acambis is based in Cambridge, UK and Cambridge, Massachusetts,
US, and is listed on the London Stock Exchange (ACM). More information
is available at www.acambis.com.

About influenza and influenza vaccines

Today, seasonal influenza represents the single largest vaccine
market in the world, worth an estimated $2.2bn and projected to grow
to $4bn by 2010(3). It is still a major global threat, which the WHO
estimates causes between 250,000 and 500,000 deaths every year around
the world(2)..Immunity against influenza viruses, whether acquired by
natural infection or immunisation, is typically transient due to the
virus´s ability to mutate and evade pre-existing immunity.
Accordingly, current licensed vaccines are updated on an annual basis
to target most effectively the presently circulating strains.

Pandemic influenza viruses are sufficiently distinct from seasonal
epidemic viruses that new vaccines must be developed to address them.
Pandemic influenza vaccines, primarily targeting avian H5N1 viruses,
are being stockpiled for emergency use. However, the efficacy of these
vaccines may be negatively impacted by continual mutations in
circulating H5N1 strains. Experts believe the next pandemic could
cause disease in two billion people. Based on best-case scenarios
modelled on the mild pandemic of 1968, this could result in two to
seven million deaths. However, if the death toll associated with the
1918 influenza virus were applied to today´s world population, there
could be 180 to 360 million deaths globally.(4)

Currently, influenza vaccines are reformulated, generally each
year, to address mutations in influenza strains (known as "antigenic
drift"). Preparations are ongoing around the world for a potential
pandemic, which would result from a major genetic change in the
influenza virus (known as "antigenic shift"). The need to change
vaccine formulations each year results in delays in initiating
vaccination programmes. In addition, it is estimated that vaccine
producers would need between three and six months to product a
strain-specific vaccine against a pandemic strain.

About ACAM-FLU-A(TM)

ACAM-FLU-A(TM) is a recombinant vaccine that uses a hepatitis B
core protein (HBc) to present M2e, the extracellular domain of the ion
channel protein M2(5). M2 is one of the three proteins expressed on
the surface of the ´A´ strain influenza virus and of infected cells
alongside haemagglutinin (HA) and neuraminidase (NA). Unlike HA and
NA, M2 is highly conserved, albeit under natural conditions not easily
recognised by the immune system. M2e could elicit an immune response
to all influenza ´A´ strains. As such, ACAM-FLU-A(TM) has the
potential to be both a universal pandemic or pre-pandemic influenza
vaccine and part of a universal seasonal vaccine. Historically,
influenza pandemics have been caused by ´A´ strains of the virus while
seasonal vaccines target both ´A´ and ´B´ strains of the virus.

References

(1) The Vietnam 2004 Clade 1 avian influenza virus has been used
by manufacturers to develop and produce pre-pandemic vaccines.
http://www.who.int/csr/disease/avian_influenza/guidelines/recommendati
onvaccine.pdf

(Due to its length, this URL may need to be copied/pasted into
your Internet browser´s address field. Remove the extra space if one
exists)

(2) WHO: http://www.who.int/mediacentre/factsheets/fs211/en/

(3) Datamonitor

(4) Kamps-Hoffmann-Preiser, Influenza Report 2006

(5) Neirynck et al., Nature Medicine, 5, 1157, 1999

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unpredictable. Forward projections reflect management´s best estimates
based on information available at the time of issue.