Acambis: Successful Phase II Challenge Trial of ChimeriVax-JE Vaccine

CAMBRIDGE, UK, Sept. 20, 2001 (PRIMEZONE) -- Acambis plc ("Acambis"), (LSE:ACM) (Nasdaq:ACAM), announces that it has successfully completed a Phase II challenge trial of its ChimeriVax-JE vaccine against Japanese encephalitis ("JE").

The primary aim of the trial was to investigate the immunological response on exposure to JE virus antigen of subjects who had previously been vaccinated with ChimeriVax-JE. The trial showed that ChimeriVax-JE induces an immune response with long-term memory and a rapid rise in protective antibodies on exposure to the virus.

The open-label, out-patient trial included 10 healthy adults who had been vaccinated nine months earlier with ChimeriVax-JE vaccine as part of Acambis' Phase I/II trial and a control group of 10 previously unvaccinated subjects. As it is not possible to challenge subjects with wild-type JE virus, an inactivated virus in the form of a registered vaccine, JE-VAX(r), was used. As an inactivated, purified, whole virus, this is recognizable to the human immune system as JE virus but is incapable of causing disease.

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

"The positive results of this Phase II trial represent an important step forward in the clinical development of a new vaccine against this life-threatening disease that affects tens of thousands of people annually. We are very pleased to see convincing evidence that ChimeriVax-JE has the potential to protect against this devastating disease."

Dr. Thomas P. Monath, Acambis' Vice President, Research and Medical Affairs, said:

"The pattern of immune response identified by this trial is an important demonstration of the effectiveness of our ChimeriVax-JE vaccine. The "memory" immune response that occurs after exposure to a virus is a critical feature of protective immunity induced by many viral vaccines, including, for example, vaccines against hepatitis. Therefore, the results of the Phase II trial provide an important immunological surrogate for demonstrating efficacy of the new ChimeriVax JE vaccine."

Notes to Editors:


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 and Canton, Massachusetts, USA. It has a broad portfolio of vaccine product candidates undergoing clinical trials and technology platforms that provide the basis for further vaccine product candidates.

ChimeriVax-JE Phase II trial results

The open-label out-patient trial was conducted in the USA under an FDA IND. Ten healthy adults who had been vaccinated nine months earlier with ChimeriVax-JE vaccine and 10 control subjects were challenged with non-infectious JE virus antigen, representing a surrogate for exposure to live virus. Serum antibody measurements were made at frequent intervals after challenges of vaccinated and control subjects. The trial established that six out of 10 subjects who had previously received ChimeriVax-JE responded with a rapid rise in neutralizing antibodies between challenge and Day 7. Of the four subjects who had no rise in antibodies during this interval, three already had protective antibody levels before challenge. Eight out of 10 subjects responded with a significant rise in antibodies by 14 days after challenge. Mean antibody levels on Day 7 were approximately 20-fold higher and on Day 14 100-fold higher than pre-inoculation levels. In contrast, none of the control subjects developed antibodies by Day 7, and only two out of 10 of the control subjects had any detectable antibody response within the 30-day observation period. Differences in mean antibody levels between the treatment groups were highly significant on all study days (P less than 0.001).

Japanese Encephalitis

Japanese encephalitis is a mosquito-borne viral disease that occurs throughout Asia and in parts of Australia. Three billion people live in regions where JE is endemic and some 14 million people travel to these regions every year from major developed countries such as the USA, Canada and Western Europe. The potential market for Acambis' JE vaccine is estimated to be around $300m a year.

This, and other news releases relating to Acambis, can be found on the Company's website at

This news release contains forward-looking statements that involve risks and uncertainties, including the timing and results of clinical trials and other product development and commercialization risks, the risks of satisfying the regulatory approval process in a timely manner, the need for and the availability of additional capital, and other risks detailed in the Company's filings with the Securities and Exchange Commission. 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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