UK company Acambis says has started Phase III trials of ChimeriVax-JE, its vaccine for Japanese encephalitis, and remains on track to file for approval of the product in 2007.

The Phase III programme will consist of two trials together enrolling 2,800 healthy volunteers. They comprise a 2,000 patient safety and an 800-strong efficacy study, testing the non-inferiority of ChimeriVax-JE against Sanofi Pasteur's approved inactivated virus preparation, JE-VAX.

Analysts at Lehman Brothers noted that the timing of the trials puts Acambis' candidate behind a rival product developed by Austrian company Intercell called IC51. The latter company initiated a 900-patient efficacy study in September, and is also planning a safety evaluation involving 4,000 patients.

In a research note, Lehman Brothers suggested that the efficacy trial designed by Acambis might be too small to satisfy US regulators. ChimeriVax-JE is an important new product for Acambis, which has seen its profits slide after the completion of a lucrative smallpox vaccine supply contract with the US Government.

Japanese encephalitis is a mosquito-borne flaviviral infection and the leading cause of viral encephalitis in Asia. The infection is a major health problem throughout Asia where 3 billion people live in JE-endemic areas.