A GP is warning that this year's flu season could see hospital wards "swamped" due to a new mutation in an old strain of the virus.
Dr John Cameron, speaking this morning to TVNZ 1's Breakfast programme, said flu cases per 100,000 of population were usually about 50, but in the USA right now, they are about 350.
What happens overseas during a flu season is often seen as an indicator for New Zealand's season, he said, which meant the importance of getting vaccinated was heightened this year.
"We could be in trouble here," Dr Cameron said.
"This is an old virus - H3N2 ... last year it did a significant shift in its protein code, and that stuffed up our vaccine.
"We want to be proactive about doing this because we're really worried about what this could do to our health system for 2018 influenza season - we could be absolutely swamped."
Dr Cameron said it is exceptionally important for people to get immunised this year, especially those who are already sick, vulnerable or pregnant.
"The vaccine is going to be available towards the end of this month and early April," he said.
The effectiveness in protecting against the flu is about 40 per cent, Dr Cameron said, which "doesn't sound great until you say 'not vaccinated is zero per cent effectiveness'.
"No, the vaccine cannot give you influenza.
"It won't cause any illness, it won't cause any damage."