A world-renowned expert in infectious diseases says there's no one-size-fits-all solution for convincing anti-vaxxers to give up their cherished beliefs and get their kids immunised - but banning unvaccinated kids from school in his home state of California has clearly been successful.
Professor Arthur Reingold, from the University of Berkeley, is an epidemiologist and infectious disease expert. The visiting Hood Fellow professor is giving a public lecture at the University of Auckland on Wednesday, looking at obstacles to vaccination and solutions from around the world.
There is overwhelming scientific consensus that vaccination has massively cut rates of mortality from infectious diseases.
Because vaccines have been so successful, many people have never seen the effects of an infectious disease outbreak - and don't appreciate the threat it would pose to their children.
"A lot of well-educated people tend to not fear the diseases we're trying to prevent, but they have fear of the vaccine itself," Reingold said.
"If that's truly your belief set and you want what's best for your child - and most people do, of course - you can understand why they would potentially make a decision we don't want them to make."
Studies have shown humans have a very poor, "skewed" understanding of risk, Reingold said. "But what's even more disturbing, to me, is that providing more information once they've formed an opinion, if anything it tends to harden the position they had originally, not convince them they were wrong."
The "Boomerang Effect" - when people harden their pre-existing beliefs when presented with contradicting information - is extremely hard to counter, he said.
"Which really speaks to the question of how do we combat this problem? Those of us who work in preventative medicine and public health think, 'Surely if we give people enough information, or counter disinformation, they'll be better informed and make good decisions'.
"And psychology has found that's not demonstrably the case."
Reingold has little in the way of fix-all solutions, though getting to people early - before they form an anti-vaccine opinion - is clearly important. It's even harder thanks to the internet.
"In many places including the United States, people are getting information and misinformation from the web, from people who have very strange beliefs."
While the stereotype is of well-off middle class parents refusing vaccines, there are many reasons parents become anti-vaccine, Reingold said.
Some poorer African American communities had very low vaccination rates, partly born of a mistrust of government following a series of highly unethical experiments last century.
What these groups do share is a distrust of the authorities, he said. Coercing people into vaccinating their children runs the risk of making that distrust worse.
In Reingold's home state of California, people who refuse to vaccinate their children often cluster together - such as in wealthy Marin County in San Francisco, and parts of Los Angeles. Some schools' vaccination rates hovered between 10-20 per cent, making herd immunity functionally zero.
in 2015, after a mass outbreak of measles at Disneyland, California cracked down, making it illegal to send kids to school or kindergarten without being vaccinated against key diseases.
Vaccination rates shot up, including in areas where clusters of people were previously strongly against the jab. But it's not clear if such a move would be effective here, Reingold said.
Last year New Zealand's then-Labour leader Andrew Little suggested unvaccinated children could be banned from childcare centres, following Australia's example, but Minister of Health Jonathan Coleman said National would not go down that track.
New Zealand is in the middle of concurrent outbreaks of mumps and whooping cough, with thousands of cases diagnosed in the past year, prompting health authorities to plead with parents to vaccinate their children.
The public lecture is on Wednesday at 5.30pm at the University of Auckland School of Medicine.