Kiwis are being urged to take health precautions to prevent infection from a deadly strain of norovirus, which is spreading across Europe and North America and has also reached New Zealand.
The Sydney 2012 variant has mutated so it is not recognisable by the human immune system, said Professor Peter White from the University of New South Wales team that identified the virus.
The virus has taken about four years to reach its current "pandemic label", said Professor White, who told Radio New Zealand he has been researching the virus with New Zealand scientists.
Those infected suffer 48 hours of severe illness including vomiting, diarrhoea, nausea, headaches and possibly fever.
"Ninety-five per cent of the New Zealand norovirus outbreaks and infections now are from the Sydney 2012 strain, and you'll get even more norovirus because it peaks in the winter."
By the time this virus has run its course in two or three years' time, more than 100,000 New Zealanders are likely to have been affected by it.
"It's very difficult to avoid unless you live in a bubble," he told the radio station.
Those infected need to take all possible precautions to stop the contagious virus from spreading to others, said Professor White.
"Don't go to work, don't visit hospitals, don't visit other people's homes, don't visit childcare centres."
The virus kills around 200,000 people around the world each year, with the very young and old and those with poor immune systems the worst affected.
There is no vaccine or treatment.
"The best defence we've got is protection and prevention from infection, so once you are infected you really do need to keep your fluids up. Rehydration is critical because if you're going to die from this virus it will be through dehydration," he said.