Acambis plc has completed a Phase I trial of its smallpox vaccine, ACAM2000. The trial assessed the safety, tolerability and immunogenicity of ACAM2000, in adult subjects who had not previously been inoculated against smallpox. All 100 subjects in the open-label trial were vaccinated with ACAM2000.

The currently accepted indication of protective immunogenicity in the case of smallpox vaccination is the development of a pock-mark on the skin, known as a "take." This "take" was the primary endpoint of the trial and was seen in 99% of the subjects. A secondary endpoint was the development of a neutralizing antibody response, which occurred in 96% of subjects. No vaccine-associated serious adverse events were observed.

Under Acambis' accelerated development programme, Phase II trials of ACAM2000 are underway and further results are expected shortly. It is anticipated that Phase III trials of ACAM2000 will begin later this year.