This initial Phase I trial tested in 56 healthy adult volunteers the safety, tolerability and immunogenicity of one of the four components in Acambis' ChimeriVax-Dengue vaccine. The component tested is known as ChimeriVax-DEN2 as it is targeted against the Dengue 2 serotype.

The trial incorporated several elements:

     -- a randomised, double-blind element in 42 volunteers compared the
        safety and immunogenicity of ChimeriVax-DEN2 at two dose levels with a
        licensed yellow fever vaccine, YF-VAX(R).  All these volunteers had
        not previously had contact with yellow fever; and
     -- an open-label portion of the trial included 14 volunteers who had
        previously received a yellow fever vaccine.  They were vaccinated with
        ChimeriVax-DEN2 to test whether prior immunity to yellow fever would
        inhibit the response to ChimeriVax-DEN2.  This is because the
        ChimeriVax technology from which ChimeriVax-DEN2 was developed employs
        an attenuated yellow fever virus as a backbone.

    The preliminary findings from the trial are as follows:

     -- ChimeriVax-DEN2 was well-tolerated at the two dose levels tested;
     -- there were no serious adverse events;
     -- 100% of subjects developed neutralising antibodies to the homologous
        Dengue 2 serotype virus within one month of vaccination and
        96% developed neutralising antibodies to a wild-type Dengue 2 virus;
     -- the seroconversion rate was similar at both dose levels tested; and
     -- prior immunity to yellow fever did not inhibit response to
        ChimeriVax-DEN2.

There are four immunologically related dengue virus serotypes, each of which needs to be represented in an effective vaccine. Acambis has successfully constructed vaccines against all four dengue virus serotypes and tested the immunogenicity, safety and efficacy of the tetravalent (four- component) vaccine in pre-clinical models. A Phase I trial of the tetravalent vaccine, ChimeriVax-Dengue, is planned for the first half of 2003.

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

"Dengue fever is a major problem across the world, with an estimated 50 million cases every year. Development of an effective vaccine to prevent dengue fever is critical for the two-fifths of the world's population who are at risk from infection and these positive trial results represent a significant step along the road to achieving that goal."

The ChimeriVax-Dengue project is funded by Acambis' partner, Aventis Pasteur, who holds worldwide rights to sales of the vaccine.

A spokesperson for Aventis Pasteur commented:

"From our Aventis Pasteur partnership perspective, these results further illustrate the attractiveness of the ChimeriVax technology for vaccine development. Aventis Pasteur is encouraged to press ahead with trials of the tetravalent ChimeriVax-Dengue."

Acambis

Acambis is a biopharmaceutical company discovering, developing and manufacturing vaccines to prevent and treat infectious diseases. It has operations in Cambridge, UK, and in Cambridge, Massachusetts, US. It has a broad portfolio of vaccine product candidates undergoing clinical trials and technology platforms that provide the basis for further vaccine product candidates.

Dengue fever

Found in most tropical and subtropical areas of the world, dengue fever is a disease caused by infection with a virus transmitted to humans by infected mosquitoes. According to the World Health Organization ("WHO"), the global prevalence of dengue has grown dramatically in recent decades and is now endemic in more than 100 countries in Africa, the Americas, the eastern Mediterranean, south-east Asia and the western Pacific. This puts two-fifths of the world's population at risk from dengue. The WHO estimates that there are approximately 50 million dengue infections each year and 500,000 cases of the more severe form of the disease, dengue haemorrhagic fever.

"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 and other product development 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.

This, and other news releases relating to Acambis, can be found on the Company's website at http://www.acambis.com .