Researchers are working on a vaccine that might one day prevent norovirus, which has made many cruise ship passengers in the United States ill. "It is possible to prevent infection and illness with a vaccine for norovirus," said Dr. Robert Atmar, a professor of medicine and molecular virology at the Baylor College of Medicine in Houston. A study of the vaccine showed promising results, HealthDay reported Friday. The study included 98 people who received either the vaccine or an inactive placebo. Of the recipients of the vaccine, 70 percent were less likely to develop the stomach bug that causes cramping, diarrhea and vomiting, and were also affected by the norovirus less frequently. The vaccine is given in two doses three weeks apart via a nasal spray. No safety issues were witnessed in the study. Side effects included stuffy nose and sneezing. Norovirus outbreaks have been reported on cruise ships docking in Tampa, Fla., and Charleston, S.C., over the past two years. A 2009 study published in the Clinical Infectious Diseases journal pointed toward poor restroom cleaning as a reason for the virus' spread. Dr. Thomas Hooton, an infectious disease professor at the University of Miami Miller School of Medicine, said the norovirus is "a mess and spreads like wildfire." "If a food handler contaminates the food on a cruise ship, it spreads like crazy. There is bad diarrhea and bad vomiting, and if they are not cleaned up properly, it can stick to surfaces and spread from person to person," Hooton said.