The sickness, brought on by the norovirus, has swept across Swedish hospitals and nursing homes in recent days causing nausea, vomiting and diarrhea and forcing the temporary closure of wards.
While a fifth of the population was previously thought to have a genetic immunity to the bug, the virus now appears to have mutated, making the entire population vulnerable to infection.
"This virus mutates all the time," Lennart Svensson, professor of molecular virology at Linköping's University told TT news agency.
"But this is the first time that we've been able to link a mutation to a change in symptoms or the spread of the infection."
Researchers at Linköping University believe anti-vomiting drugs given to patients receiving radiation treatment may provide a treatment for the worst symptoms of the bug.
"We think that the same nerves cause the vomiting, both in cancer treatments and in patients with the winter vomiting bug," said professor Svensson.