Using new methods to make influenza vaccines instead of the current egg-based approach could cut production time in half in case of an outbreak of deadly avian flu, U.S. researchers said on Wednesday.

The team at the University of Michigan proposed a system for refitting biopharmaceutical facilities for quick production in the event of such an outbreak.

U.S. health officials have said it would take months to manufacture a vaccine against the H5N1 avian flu strain should it cause a human epidemic.

The method is tricky and uncertain and requires the use of specially chosen chicken eggs in which to incubate the virus for months.

Experts know using cell cultures in lab dishes would be quicker. Henry Wang, a University of Michigan professor of biomedical and chemical engineering, says he has calculated how much quicker.

Building a separate cell culture facility and shipping the cell to the existing biomanufacturing plants could cut the production cycle in half to two months, he told a meeting of the American Chemical Society in San Diego.

Wang identified a dozen potential facilities around the world that were already approved by the U.S. Food and Drug Administration and could be modified to manufacture flu vaccines in an emergency.

Many already use mammal cell cultures to produce their drug products, so they could easily be switched to producing flu vaccine, Wang said.

H5N1 has killed millions of birds in Asia and 47 people in Vietnam, Thailand and Cambodia since the end of 2003. It has not acquired the ability to spread easily from person to person, although health officials consider that a likely possibility.

In that case, it could kill millions of people around the world in a very short time.