An experimental vaccine for the viral gastrointestinal infection norovirus has been bioengineered in a tobacco plant, scientists said Tuesday.

The method could offer more efficient and cheaper ways to bring vaccines to the public quickly, researchers say.

Bioengineered viruses in plants are decoys that are harmless to humans, said Charles Arntzen, a professor at Arizona State University in Tempe.

"When you immunize people with it, the immune system says, 'Oh, I'm being invaded by a norovirus,'" Arntzen said. "You get a full blown immune response which will protect you from subsequent exposure to the disease."

Arntzen presented his findings Tuesday at the American Chemical Society's annual meeting in Washington, D.C.

In the study, Arntzen and his colleagues created a vaccine for norovirus, which causes severe diarrhea or nausea for up to three days.

Arntzen believes plant biotechnology is well suited for mutating viruses like norovirus and flu.

The norovirus group of viruses affect the human gastrointestinal system, and were previously called Norwalk-like virus, according to the Public Health Agency of Canada.

Norovirus is not as life-threatening as the flu, but it can force wings of hospitals, schools, daycare centres and nursing homes, navy and cruise ships to shut down for cleanups, with major economic consequences.

Inhale vaccine

In the study, researchers engineered plant viruses to produce high levels of virus-like nanoparticles in tobacco plants.

The particles contained the outer surface protein of the norovirus that is recognized by the human immune system, but did not have any of the infectious material from the virus.

After successful experiments in mice, the researchers are developing a nasal delivery system for the virus-like particles, rather than injecting the vaccine. So far, they've only done proof of concept research in humans and expect to launch Phase 1 clinical trials in humans late this year or early in 2010.

Building greenhouses to grow plant-based vaccines could be cheaper than sterilized facilities needed to manufacture insect or mammalian cell cultures used in most traditional vaccines, and would also be cheaper to purify, Artnzen said.

The Alberta Research Council helped pioneer plant-based pharmaceuticals.

"You can harvest the seeds," said Jürgen Quandt, a microbiologist with the council. "You can multiply it 10 times, 100 times over, and thereby really very quickly fulfil any anticipated demand."

Similar products are working their way through the U.S. Food and Drug Administration's approval process, Artnzen said.

Sources of norovirus include person-to-person contact, contaminated shellfish, water and ice. Doctors say handwashing and sanitizing are the best method for preventing the spread of the virus.