Psychologist Nigel Latta has weighed in on the psychology behind the anti-vaccination campaign as a measles outbreak takes hold in Christchurch.

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Parents of unvaccinated children are being urged to keep them out of school, so they don't spread the disease.

TVNZ1's Seven Sharp asked Latta why do people jump on board the anti-vax hysteria?

"If it was just about facts everyone would vaccinate their children, because if your child catches measles they have a one in 1000 chance of dying from it.

"However, if they have a vaccine there is a one in one million chance of having a serious reaction to the vaccine and dying," Mr Latta said.

He then went on to say the anti-vaxers are good at creating "fear" on social media and normally rationale people buy into the idea.

"Our brains have an emotional reaction to stuff first, and people will say it either feels right or I don't have a good feeling about vaccinations.

"It shouldn't be about feelings it should be about the numbers, the numbers overwhelmingly say that you should vaccinate your children," Mr Latta said.

On the situation in Christchurch, Latta says there are people putting their own children and others at risk by not getting their kids vaccinated and letting them go to school.

He likened anti-vax campaigners to being as legitimate as those at the Flat Earth Society.