Anti-vax sentiment is becoming more entrenched among nearly a third of Kiwis – a worrying trend one leading scientist has blamed on a social media-driven "misinfodemic".
The findings, published by University of Auckland researchers, come from the first longitudinal survey to track Kiwis' attitudes to vaccination over time.
While 60 per cent of those surveyed remained highly confident vaccines were safe, the study also found 30 per cent were growing more sceptical.
The paper - using data from the 20-year New Zealand Attitudes and Values Study, which regularly polls more than 18,000 Kiwis on various topics – looked at perceptions on vaccination between 2013 and 2017.
"The data did show a quite high number - 30 per cent - of people who are less supportive of vaccination now than they were five years ago and the danger is that trend will continue, which poses a challenge in terms of public health messaging," lead author Carol Lee said.
Survey participants were asked how strongly they agreed or disagreed with the statement "It is safe to vaccinate children following the standard NZ immunisation schedule" on a scale of between one and seven, with a seven denoting strong agreement.
Respondents split on the vaccination question fell into distinct groups.
"Believers" tended to agree with the statement at the upper end of the scale and made up 60 per cent of the total, while "sceptics" made up 30 per cent and generally agreed at less than five on the scale, while also showing a falling level of agreement over time.
The study also turned up another group of 10 per cent who had become more positive about vaccination in the past five years.
It further pointed to some general trends among demographics: Europeans, men, those from richer areas and those with a higher education level were more likely to be "believers".
Older individuals, women, and those with a generally lower level of education, on the other hand, were more likely to be vaccine sceptics.
"Based on previous studies, it is likely that factors such as disparities in healthcare access, vaccine knowledge or ability to interpret vaccine information and trust in health professionals contribute to differences in confidence levels across demographic groups."
The Immunisation Advisory Centre's director, Associate Professor Nikki Turner, said there was still mixed evidence on which groups were more likely to oppose vaccination.
Studies had pointed to wealthier and highly educated people who didn't hold science degrees but also to poorer, less-educated people distrustful of the Government and health officials.
"These people tend to be grouped in areas and localities, and not spread evenly throughout the country but we think some of the issue is like-minded people grouping together, and also the magnification effect of social media."
While the issue was once largely limited to coffee groups, it had been amplified by platforms like Facebook, where sceptics could network and share misinformation widely without being challenged.
While the latest data around absolute immunisation decline rates showed some recent increases, these had been generally small, within the order of a few percentage points.
Coverage tables still showed 89 per cent of 5-year-olds were fully immunised for their age, along with 92 per cent of 1-year-olds – and the missing cohorts weren't just down to parents refusing vaccination, but also families with barriers to healthcare.
Still, Turner said, anti-vaccination sentiment remained a "huge challenge" here and overseas - and one that would become all the more important if a vaccine was found for the new coronavirus.
"We are living in an age of the misinfodemic, where information flows abundantly but not all of it is true," said Associate Professor Helen Petousis-Harris, a vaccinologist at the University of Auckland.
"Some information is deliberately manufactured into dangerous conspiracy theories. We are seeing polarisation on many issues all over the world and it is both disturbing and dangerous."
She saw a two-fold solution to the problem.
"First, ensure people leave school with a basic understanding of logic and how the scientific method works so they can safely navigate the deluge of information."
Second, health authorities could keep better track of people's concerns online – and keep them informed with honest and transparent messages.
"Don't leave a void to be filled by misinformation and conspiracy theories."
• Reliable information on vaccines can be found here.