Acambis plc announces preliminary results from a phase 2 trial of its Modified Vaccinia Ankara (MVA) smallpox vaccine, MVA3000. Acambis is co-developing MVA3000 with Baxter Healthcare SA, which is providing process development and manufacturing services.

MVA3000 is an attenuated smallpox vaccine that is being developed for use in people for whom the traditional smallpox vaccine is contraindicated, such as patients with disorders of the immune system or skin conditions such as eczema. Acambis was awarded contracts by the US National Institute of Allergy and Infectious Disease (NIAID), part of the US National Institutes of Health, in February 2003 and September 2004 for the manufacture of MVA3000 and a series of phase 1 and phase 2 clinical trials.

In total, 590 healthy adult subjects were enrolled in this randomised, double-blind, placebo-controlled phase 2 trial, which tested multiple dose levels of MVA3000 against placebo. Of the enrolled subjects, 361 had never received a smallpox vaccine (i.e., were "vaccinia naïve"), and 229 had previously been vaccinated against smallpox. This was the first trial in which the safety and immunogenic of MVA3000 had been tested in subjects previously vaccinated against smallpox.

In vaccinia naive subjects vaccinated at the highest dose level, immunogenicity results were consistent with the findings from the phase 1 trial of MVA3000 with 75 per cent of subjects seroconverting after two doses. In previously vaccinated subjects, 88 per cent of subjects vaccinated at the highest dose level seroconverted after two doses. The neutralising antibody levels necessary to protect against smallpox are unknown.

No subjects experienced vaccine-related serious adverse events and most of the adverse events were mild or moderate in nature. Despite active solicitation of cardiac-related adverse events, no subjects were diagnosed with myocarditis or pericarditis during this study. Among the subjects receiving MVA3000, the most commonly reported adverse events were events traditionally associated with smallpox vaccination and included injection site reactions (pain, redness, swelling and itching), headache, fatigue, malaise and muscle ache.

CEO Gordon Cameron commented, "With these phase 2 clinical trial results, we achieve another milestone in our programme to develop MVA3000. Both the safety and immunogenic results are in line with our expectations about MVA3000, with the results from our phase 1 trial of the vaccine and with previous data on other MVA vaccines."