New Zealand has reached an unwanted milestone in the battle against measles.
There have now been more than 1000 cases confirmed since the outbreak began.
Auckland is still the epicentre of the response, but there's a spike in cases in Queenstown that's causing concern too.
"We only have a small number at the moment, but we're conscious this could spread quickly," Southern medical officer of health Dr Susan Jack told Newshub.
The US has started warning travellers to New Zealand of the risks.
It comes as immunisation experts gather in Auckland for the annual Immunisation Conference.
People from the US are now being warned to ensure they're vaccinated before travelling to New Zealand.
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Professor Kathryn Edwards, of the Vanderbilt University in Tennessee, said what's worrying is the level of hospitalisation rates here are three times higher than the US.
"I think that the severity of measles in New Zealand appears to be greater than what we are seeing in the United States."
Experts in New Zealand are unsure why, but it could in part be due to emerging strains.
But Professor Edwards said quick action can stop it.
"If you are exposed to measles and you get a vaccine within 72 hours - you can prevent it from becoming a disease."
In the south, that's what experts are working on to avert an outbreak spreading there.