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Acambis’ JE vaccine meets and exceeds primary endpoint in pivotal Phase 3 efficacy trial

02 Mar 2007

Acambis plc announces that its investigational single-dose vaccine against Japanese encephalitis (JE), ChimeriVax™-JE, has met and exceeded the primary immunogenicity endpoint in a pivotal Phase 3 efficacy trial.

CAMBRIDGE, UK and CAMBRIDGE, MA, USA | Mar 01, 2007 | Acambis plc (Acambis) (LSE: ACM) announces that its investigational

single-dose vaccine against Japanese encephalitis (JE), ChimeriVax™-JE, has met and exceeded the primary immunogenicity endpoint in a pivotal Phase 3 efficacy trial.

In the randomised, double-blind, multi-centre Phase 3 study, 820 adult subjects were vaccinated at a 1:1 ratio with either Acambis' single-dose ChimeriVax-JE or JE-VAX®, the licensed three-dose JE vaccine. The trial was designed to compare the immunogenicity 30 days after immunisation with a single dose of ChimeriVax-JE or with three doses of JE-VAX. The subjects received either two doses of placebo (saline) followed by one dose of ChimeriVax-JE or the full three-dose schedule of JE-VAX.

The primary efficacy endpoint, seroconversion rates based on neutralising antibodies against the relevant homologous JE virus, was met, demonstrating the non-inferiority of ChimeriVax-JE to JE-VAX. Of the subjects vaccinated with ChimeriVax-JE, 99.1% of subjects seroconverted compared with 74.8% of subjects in the JE-VAX group. The efficacy of ChimeriVax-JE was also shown to be statistically superior to JE-VAX (p <0.05). In addition, ChimeriVax-JE elicited a rapid immune response, with 93.6% of those vaccinated with ChimeriVax-JE generating neutralising antibodies 14 days after vaccination.

The primary safety objective of the study compared the safety and tolerability of ChimeriVax-JE and JE-VAX. There were no vaccine-related serious adverse events observed during the 60-day treatment observation period. The overall incidence of adverse events following vaccination was slightly lower in the ChimeriVax-JE group than in the JE-VAX group. Additionally, the incidence of local injection site reactions in the ChimeriVax-JE group was statistically significantly lower than in the JE-VAX group. The majority of adverse events in those vaccinated with ChimeriVax-JE were mild or moderate in nature. These data will be added to those already generated from the Phase 3 safety trial, results of which were announced in October 2006.

Acambis' Chief Executive Officer Gordon Cameron commented:

“These are remarkable results, surpassing even our high expectations of ChimeriVax-JE. The data clearly support the benefits of a live, attenuated vaccine approach – single-dose administration, rapid immunity and high immunogenicity. When combined with the excellent safety profile shown by the data from both this trial and the Phase 3 safety trial in 2,000 subjects completed last year, we believe that ChimeriVax-JE is ideally placed to address the very real global health need for a safe and effective single-dose JE vaccine."

These Phase 3 data will support filings for both the endemic and the travel vaccine markets.

Acambis recently entered into a partnership agreement with sanofi pasteur, the vaccines business of the sanofi-aventis Group, for the worldwide marketing and distribution of ChimeriVax-JE, excluding India, the Indian subcontinent and the US. Sanofi pasteur, a world leader in vaccines, plans to introduce ChimeriVax-JE in Europe and throughout the Asia Pacific region, with particular focus on the large endemic countries, including Thailand and China.

In India and the Indian subcontinent, Acambis has partnered with Bharat Biotech International Limited, a leading Indian biotechnology company, and is currently conducting a paediatric clinical trial of ChimeriVax-JE in India, where the target population for a JE vaccine is predominantly children.

-ends-

Enquiries:

Acambis plc
Gordon Cameron, Chief Executive Officer
David Lawrence, Chief Financial Officer
Lyndsay Wright, VP, Communications and IR
Tel: +44 (0) 1223 275 300

Brunswick
Jon Coles / Justine McIlroy / Margherita Lupi
Tel: +44 (0) 20 7404 5959

Notes to editors:

About Japanese encephalitis
Japanese encephalitis is a disease caused by a mosquito-borne flavivirus that affects the
membranes around the brain. Most JE virus infections are mild (fever and headache) or without
apparent symptoms but approximately one in 200 infections results in severe disease
characterized by rapid onset of high fever, headache, neck stiffness, disorientation, coma,
seizures, spastic paralysis and death. The case fatality rate can be as high as 60% among those
with disease symptoms. Around 30% of those who survive suffer from lasting damage to the
central nervous system. In areas where the JE virus is common, encephalitis occurs mainly in young children.

According to the WHO, approximately 30,000 to 50,000 people suffer from JE annually, mainly in
Asia. During a recent epidemic in northern India and Nepal, JE killed more than 1,000 people, most of them children. An estimated three billion people live in JE-endemic regions, which include Thailand, China, Japan, India and parts of Australia.

About ChimeriVax-JE
• ChimeriVax-JE is being developed to provide a safe, single-dose JE vaccine for travellers
and those living in JE-endemic regions.
• It is a live, attenuated, injectable vaccine and was developed using Acambis' proprietary
ChimeriVax™ technology.
• Clinical results show that Acambis' ChimeriVax-JE requires only one dose for adequate
protection against JE versus two or three required with other JE vaccines.
• In previous trials, subjects vaccinated with ChimeriVax-JE exhibited an immune response
with long-term memory and a rapid rise in protective antibodies on exposure to the virus.
• Acambis has recently initiated a Phase 2 paediatric trial in India.
• In the phase 3 efficacy trial, the primary endpoint was the non-inferiority of the
seroconversion rate to the homologous vaccine virus of subjects given ChimeriVax-JE compared with the seroconversion rate to the Nakayama virus of subjects given JE-VAX. In October 2006, Acambis announced an overall blinded seroconversion rate to ChimeriVax
JE virus for all subjects combined.

Phase 3 safety trial
Acambis announced results from a pivotal Phase 3 multi-centre safety trial of ChimeriVax-JE in October 2006. Results showed that the total number of subjects reporting adverse events was comparable between subjects vaccinated with ChimeriVax-JE and those who received placebo, and that vaccination with ChimeriVax-JE was systemically and locally well tolerated. There was one serious adverse event considered to be vaccine-related. This event, febrile illness, resolved without complications. The majority of adverse events were mild or moderate in nature, with headache and fatigue being the most frequently reported events

About ChimeriVax
ChimeriVax was developed jointly by Acambis and St Louis University and has been used by Acambis to develop vaccines against Japanese encephalitis, West Nile and dengue. Acambis has held an exclusive worldwide licence to the technology platform from St Louis University since 1997. The technology uses a live, attenuated strain of the yellow fever virus as a backbone into which elements of the target virus are introduced to create new “chimeric" viruses as vaccines. These vaccines have the potential to safely and effectively elicit protective immune responses after only a single dose. Sanofi pasteur has licensed another ChimeriVax-based vaccine from Acambis, ChimeriVax-Dengue.

About Acambis
Acambis is a leading biotechnology company targeting infectious diseases with novel vaccines. Acambis' development-stage pipeline includes vaccines that could either offer improvements over existing products or target unmet medical needs. As well as ChimeriVax-JE, Acambis' proprietary ChimeriVax technology has also been used to develop ChimeriVax-West Nile, which is undergoing Phase 2 clinical testing, making it the most advanced investigational vaccine against the West Nile virus. Acambis also has the only vaccine in development against Clostridium difficile, a leading cause of “superbug" hospital-acquired infections. Recognised internationally as the leading producer of smallpox vaccines, Acambis is developing an investigational smallpox
vaccine, ACAM2000, and is manufacturing emergency-use stockpiles of this investigational vaccine for the US Government and other governments around the world.

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.

“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 management' in the Company's 2005 Annual Report and “Risk factors' in its Form 20-F, in addition to those detailed on the Company's website and 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.

SOURCE: Acambis plc

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