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Taking a Shot at Sinking the 'Cruise Ship' Virus

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WebMD Health News
Reviewed by Louise Chang, MD

Sept. 13, 2012 (San Francisco) -- An experimental vaccine shows promise for protecting people against a nasty stomach virus known for causing outbreaks of diarrhea and vomiting on cruise ships, in nursing homes, and in other close quarters.

The research is very early and much more testing is needed. But the injectable norovirus vaccine cleared its first hurdle, proving safe and stimulating an immune response in a study of about 75 healthy adults.

Norovirus is responsible for about half of all outbreaks traced to contaminated food or water. It causes 21 million cases of acute gastroenteritis (stomach flu) per year in the United States.

"You really can't do anything while it runs its course," says researcher John Treanor, MD, chief of the infectious diseases division at the University of Rochester Medical Center in New York.

Nasal Vaccine

Last year, researchers tested a nasal spray vaccine in 90 volunteers. About a third of those who got the vaccine developed symptoms such as diarrhea and vomiting related to norovirus, compared with about two-thirds of those who got a placebo vaccine.

The results were good, but not good enough, Treanor says. Researchers believe that may be because there are multiple genetic strains of norovirus. The nasal vaccine only worked against one of them. 

The new vaccine, given as a shot in the arm, works against two, resulting in a cross-reaction that provides added protection.

The research was presented here at the annual infectious diseases meeting of the American Society for Microbiology.

Studies of both vaccines were funded by LigoCyte Pharmaceuticals, a research company in Bozeman, Mont. Treanor consults for the company as well as for several other pharmaceutical firms.

Injectable Vaccine

In the new study, volunteers received two injections of vaccine or placebo four weeks apart.

The vaccine was generally well tolerated, with pain and tenderness in the area of the injection being the most common side effects. There were no serious side effects related to use of the vaccine, Treanor says.

The researchers used blood tests to check for evidence of virus-fighting antibodies.

"Compared to placebo, volunteers of all ages mounted a rapid antibody response," he says. The second dose did not appear to give additional protection, "which may mean that only a single dose is needed."

The next step is to show that people who get the vaccine have fewer symptoms than those getting a placebo. Treanor believes the results will be better than those seen with the nasal spray, as the new vaccine stimulated a stronger response.

The results are promising, but there remain a number of major challenges to developing an effective norovirus vaccine, says Hoonmo Koo, MD, an expert on noroviruses from Baylor College of Medicine in Houston. He was not involved with the study.

"How long will the protection last?" he asks. When you recover from norovirus, natural immunity only lasts about 14 weeks, and there's not even complete immunity -- just a lower risk of getting sick again," Koo points out.

Still, "if you're going on a cruise, you only need two weeks of protection," Treanor says.

Also, the dominant strain changes from year to year. So, as with the flu virus, there needs to be active surveillance so each year's vaccine will be effective against that year's strain, Koo says.

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