Karolinska Institutet Oct 24 2025 Winter vomiting disease is caused by the Norovirus, which is most virulent during the colder half of the year. The infection clears up after a couple of days, but the protection it provides is short-lived, meaning that the same person can fall repeatedly sick in a short space of time. But some people cannot succumb to the virus, thanks to a particular gene variant. "We wanted to trace the historical spread of the gene variant," says Hugo Zeberg, senior lecturer