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ACAM2000 Smallpox Vaccine Phase 3 Trials COmpleted, Move Towards Submission of BLA

September 20, 2004 -- Acambis plc ("Acambis") announces an update on its programme to develop a second-generation smallpox vaccine, ACAM2000.

In April 2004, Acambis announced that its two Phase 3 trials of its investigational second-generation smallpox vaccine, ACAM2000, had been placed on clinical hold by the US Food and Drug Administration ("FDA") following the discovery of suspected cases of myocarditis in three subjects. Myocarditis is a condition involving inflammation of the heart muscle.

The two Phase 3 clinical trials were designed to compare the safety, tolerability and efficacy of ACAM2000 with Dryvax®, the currently licensed smallpox vaccine. The first Phase 3 trial involves subjects who have never received smallpox vaccine. The second Phase 3 trial involves subjects who have previously been vaccinated against smallpox. In each of these trials, the ratio of individuals receiving ACAM2000 or Dryvax® was 3:1.

Acambis carried out an extensive review of safety data from both trials. The detailed safety data were then reviewed by the Data Safety Monitoring Board ("DSMB") that oversees Acambis' smallpox vaccine trials and an independent expert Cardiology Advisory Panel ("CAP"). In total, eight cases of myocarditis were identified among the 1,162 subjects naive to smallpox vaccination who had received either ACAM2000 or Dryvax®. All eight subjects have returned to their normal activity and will be followed for 12 months after vaccination. No myocarditis cases were identified in the Phase 3 trial involving 1,819 subjects who had previously received a smallpox vaccine.

In its response to the clinical hold, Acambis submitted the findings and recommendations from the DSMB and CAP safety reviews to the FDA, together with blinded efficacy data. Acambis' response recommended that the trials be closed to further enrolment because the data collected so far should be sufficient to allow the assessment of the vaccine's safety and immunogenicity (induction of an immune response likely to protect against smallpox) and because recruiting more subjects would be unlikely to reveal additional information of value to the further understanding of adverse events or immunogenicity.

The FDA recently notified Acambis that the clinical hold for these studies has been removed and that the FDA concurs with Acambis' recommendation to close the trials and complete analysis of the ACAM2000 clinical trials at this point. Acambis now plans to proceed toward the compilation and submission of a Biologics License Application ("BLA") for ACAM2000 based upon the data obtained in all ACAM2000 trials conducted to date, including clinical data from more than 2,900 subjects already vaccinated in the Phase 3 trials.

Acambis is working with Baxter Healthcare Corporation, part of Baxter International, Inc., to manufacture its investigational ACAM2000 for the US and other governments, under the FDA's Investigational New Drug application for ACAM2000.

Gordon Cameron, Chief Executive Officer of Acambis, welcomed the clarity that the FDA's decision had provided, and said:

"Acambis is pleased to be progressing on the path forward for our ACAM2000 smallpox vaccine programme. We are now assembling the data required for the BLA, and plan to submit the application in 2005."

Source: Acambis

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