There are urgent calls for people to vaccinate themselves against measles to protect others.
Five Cantabrians have been confirmed with the virus in the past week, the latest a pre-schooler from Rangiora.
Dr Nikki Turner of the Immunisation Advisory Centre says most young people receive the MMR (measles, mumps, rubella) vaccination at a young age - but not all.
"There's a group of people in our community who are unable to be vaccinated because of weakened immune systems, such as children recovering from cancer treatment and things like that."
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Dr Turner says people should get vaccinated if they have no record of an initial vaccination - even if they think they might have had one before.
"For anybody who's not sure of their immunisation history, go and check - or just go and get another vaccination. It's perfectly safe to get revaccinated."
The chance of a wider outbreak is low, she says, with most Kiwis up-to-date on their vaccinations.
"There is actually no measles spreading in New Zealand itself - all the cases are coming in from outside. But if we do not have enough people vaccinated, it will spread."
One person in Auckland has been diagnosed recently, with a further 150 possibly at risk.
"One in 10 people with measles need hospital treatment and the most serious cases can result in deafness or swelling of the brain," Medical Officer of Health Jay Harrower said last month.