UK biotechnology company PowderMed has asked for approval to start clinical trials of a ‘rapid response’ vaccine for the H5N1 strain of avian influenza.

Although other vaccines against H5N1 are further forward in development, PowderMed believes that its candidate, which is based on viral DNA, could have an advantage in terms of speed of production over vaccines made in either eggs or cell culture-based systems.

The plasmid DNA for PowderMed's vaccine is produced using a bacterial fermentation process that could carve the production time down from nine months with egg-based systems to a matter of weeks, which could make for rapid production of vaccine in response to a rapidly-emerging pandemic strain.

If the strain of virus causing an influenza pandemic mutated, it would be relatively simple to isolate the new strain, get hold of its key DNA sequences and produce new vaccine. Moreover, the use of DNA means that limited supplies of vaccine antigen can be stretched further: PowderMed estimates that 1 kg of H5N1 DNA could be manufactured in just three months and provide enough antigen to vaccinate the UK population of 60 million people twice over.

PowderMed aims to carry out the trial at a clinical research centre in London, which is already involved in recruiting patients for flu vaccine trials. It hopes the findings will back up results from a US study of a seasonal flu vaccine, reported in the journal Vaccine, which showed that the vaccine achieved 100% efficacy in stimulating antibodies against the virus.

Information on the trial published on the website indicates that it will enroll a target group of 75 adult volunteers and is scheduled to get underway this month, with completion in May 2007. It will look at four different doses of the vaccine, given as a prime-boost regimen on days 0 and 28.

The vaccine takes the form of microscopic gold particles, coated with DNA, that are shot through the skin and penetrate local immune cells in order to stimulate a response.