Singapore: Even as a new strain of stomach flu is infecting many across the world, scientists in Japan seem to have made progress in vaccine development.

Early stage human studies on a vaccine against norovirus that has been identified as the main source of gastroenteritis on cruise vessels will conclude this year, claimed an Associated Press report. The report went on to explain that it might take the vaccine several years to be available for sale.

Rajeev Venkayya, Head of Vaccine, Takeda Pharmaceutical has said that a course of injections could provide lifelong protection against 95 percent of strains. Takeda's vaccine is the most developed of several immunization programmes under current research

As per the Center for Disease Control and Prevention data, 21 million people are infected in the US annually this highly contagious illness. About 800 deaths take place, mostly the very young and the elderly.

"Norovirus also known as the winter vomiting bug, can be caught from an infected person, contaminated food or water, or by touching contaminated surfaces, causing the stomach and intestines to become inflamed, resulting in pain, nausea, diarrhoea, and vomiting," the Center for Disease Control and Prevention warned.

If Takeda's norovirus vaccine is approved, analysts believe it would create potential annual revenue of about $US400 million.

"Takeda's vaccine combines viral components from two norovirus types that laboratory studies suggest should fight all strains known to have circulated during the past 20 years, including the Sydney one, with studies of the vaccine in healthy volunteers beginning in May 2012, with plans for further tests in children and the elderly and a larger study to gauge the efficacy of one or two shots, and it will be several years before the vaccine is ready for sale," Rajeev Venkayya said.