The trans-Tasman bubble is thought to be responsible for the re-emergence of the nasty flu-like virus, RSV.
Five hundred people around the country - many of them children - have RSV and hospitals are postponing operations to free up beds.
Otago University virologist, Lance Jennings, told Mike Hosking RSV generally causes outbreaks during winter in New Zealand every year and overseas.
He says what's unusual about this year is the virus didn't circulate at all last year.
“Probably a result of a lockdown last year and travellers coming from overseas having to be in isolation for fourteen days before interacting with people in our community.”
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