The vaccine in capsule form gives it an advantage over other oral cholera vaccines, the scientists said in the latest issue of the Proceedings of the National Academy of Sciences.

"One advantage is refrigeration is no longer required, and it's more friendly (and safe) without the use of needles," said Hiroshi Kiyono at the University of Tokyo's Department of Microbiology and Immunology.

"It has proven effective in producing antibodies in mice, which have neutralising activities against toxins," he said.

Rice protein is also stable in an acidic environment and can withstand digestion in the stomach. This ensures the vaccine is delivered into the intestine where it is needed to trigger an immune response to fight cholera bacteria.

Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae, which has a short incubation period from less than a day to five days. It causes copious, watery diarrhea and vomiting that, without prompt treatment, can quickly lead to severe dehydration and death.

Currently there are oral and injectable vaccines but most of them require refrigeration, which is prohibitively expensive in the places that need the vaccine most.

Kiyono and his colleagues plan to test the efficacy of their vaccine next in primates.