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 was the primary endpoint of the trial. A "take" was seen within 10 days after vaccination in 100% of ACAM1000-treated subjects and 97% of Dryvax-treated subjects. The size and appearance of the "takes" were identical across treatment groups. No serious or unexpected adverse events were reported in the ACAM1000 group, whereas one subject in the Dryvax group developed a non-healing pock at the site of inoculation.

The results of this Phase I trial will be presented by Dr Thomas Monath, Chief Scientific Officer, at a meeting of the G7 Global Health Security Action Group being held at the Paul-Ehrlich-Institut in Langen, Germany on 5-6 September.

Following these encouraging results, a second, open-label trial has been initiated in which 70 subjects are being given ACAM1000 to test further the vaccine's safety and immunogenicity. Results from this second trial are expected to be available shortly.