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The principal of a Northland school with up to 250 unimunnised students says he knows of at least six families who will not let their children be vaccinated because they don't believe in it.
Northland has had two confirmed cases of measles - which is highly contagious and can prove fatal - in the past two weeks.
With the region having some of the lowest immunisation rates in the country, that's left health officials scrambling to ensure it doesn't spread - and principals are being encouraged to exclude students who haven't had their jabs.
But schools say it's just not practical to keep potentially thousands of children out of classrooms - and parents need to get their children immunised immediately to avert a crisis.
Horahora school principal Pat Newman says it's possible some of the 250 students at his school who don't have immunisation certificates have actually had their jabs, but have lost the paperwork.
He knows that's not the case for everyone, though, and he's trying to get word out to parents about the urgency and the seriousness of the situation.
"The odds of a child dying from measles are one in 1000 - the odds of one dying from being immunised are way, way, way out from that."
Education Minister Chris Hipkins earlier today said he did not think pupils who had not been vaccinated should be excluded from classes, but criticised those who refused to vaccinate, saying they were "pro-plague".
The Education Ministry also confirmed that schools cannot bar unimmunised children unless they are instructed to do so by health authorities.
It was only children who were believed to have a communicable disease that could be prevented from attending.
Northland DHB has asked schools to consider excluding unimmunised children, but the Education Ministry said the Northland Medical Officer of Health had not asked any school to close or exclude students.