DNA vaccines, they say, can be produced more rapidly than conventional vaccines and could possibly save thousands of lives if a global influenza outbreak occurs.

A DNA-based vaccine could be a potent weapon against this emerging threat, particularly if enough conventional vaccine isn't available, according to Peter Dunnill, DSc., and his colleagues at University College London.

However, they caution that any DNA vaccine should only be used as needed to slow the spread of the disease because the technique is largely untested in humans. The analysis appears in the November-December issue of the journal Biotechnology Progress, a co-publication of the American Chemical Society and the American Institutes of Chemical Engineers.

The avian virus, H5N1, has spread among birds throughout Southeast Asia and has been recently detected in Eastern Europe. The virus has killed more than 60 people in Asia since 2003 and forced the slaughter of millions of birds. There are no confirmed cases of human-to-human transmission of this flu, but that could change as the virus continues to mutate, Dunnill says.

If that occurs, current production facilities are unlikely to meet global demands for conventional vaccines in time to avert a pandemic, Dunnill says. But it might be possible to quickly produce a DNA vaccine by adapting the manufacturing processes of selected biopharmaceutical and antibiotic plants in countries such as the United States, China and India.

"A DNA vaccine is not a panacea, however it could be useful if the situation gets out of hand," Dunnill says. "But if we're going to try it, we need to move. You can't expect to walk into a production facility, hand over the instructions, and expect them to make it on the spot. It's going to take some weeks, and we really don't know how much time we have."

A DNA vaccine could be produced in as little as two or three weeks, Dunnill says. To do it, scientists would create a "loop" of DNA that contains the construction plans for a protein on the outer surface of the H5N1 virus. When that DNA is injected into cells, it would quickly reproduce the protein and trigger immunization in much the same way as a conventional vaccine.

In contrast, producing conventional vaccines from viruses incubated in fertilized eggs can take up to six months, which is too long to effectively prevent an influenza pandemic, Dunnill says.

Although no commercial influenza DNA vaccine is currently available, these vaccines have worked well in animals. However, human trials are still in the early stages so the safety and efficacy of these vaccines isn't fully established in people.

But these trials could be accelerated, Dunnill says, particularly if the H5N1virus eventually causes large numbers of human deaths and out paces the supply of conventional vaccine. In the worst case scenario, he suggests, using a DNA vaccine could be a "stop-gap" measure until enough conventional vaccine is available to corral the pandemic.

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