'Anti-vaxxers' who feel they will be judged for their decision are keeping it a secret, putting others at greater risk, a new study suggests.

Key points: Parents fear judgement when sharing decision not to vaccinate children

Parents fear judgement when sharing decision not to vaccinate children Trend putting pregnant women and newborns at risk, study says

Trend putting pregnant women and newborns at risk, study says Expert says shaming is not an effective way to raise vaccination rates

Expert says shaming is not an effective way to raise vaccination rates AMA says lack of vaccination an "immense frustration"

Edith Cowan University school of psychology and social science researchers said the study showed the health of pregnant women and newborns was at risk from parents who refused to be honest about their decision not to vaccinate their children.

Lead researcher Dr Bronwyn Harman told The Guardian it was important to understand the reasons parents were not vaccinating their children.

"It really does frighten me a lot if people coming into contact with those women and children aren't disclosing their status out of fear of being perceived as bad parents," she said.

Early results from the study indicate reasons included a mistaken belief a healthy diet alone could protect their children as well as herd immunity.

But mainly, feelings of manipulation by governments was driving under-vaccination, Dr Harman said.

"These parents believe they are being lied to and believe they have done enough of their own research to believe vaccinating is risky, even though much of their research comes from unreliable sources on the internet."

Australian Childhood Immunisation Register data shows as at September 30 last year 93 per cent of children aged 12 to 15 months were fully immunised. For children aged two years to 27 months, the rate dropped to 90.4 per cent.

An Australian study published in journal Vaccine last year found that of the infants incompletely immunised, just 16 per cent had mothers who disagreed with immunisation.

It reported other "barriers" associated with under-vaccination included low levels of social contact, health issues, large family size and not using formal childcare.

University of Sydney paediatrics expert Professor Nicholas Wood said promoting shame among parents who did not vaccinate was not an effective tactic to improve vaccination rates.

"Driving all to feel shamed is not the ideal way to promote vaccine uptake," Associate Professor Wood, who is also from The Children's Hospital at Westmead, told the ABC.

"The anti-vaxxers are likely to believe it is just more of an attack on their choice.

"What we need to do is to tackle the wide range of reasons that the 'not very many' are not vaccinated in an open and individualised way, remove shame and lessen confusion."

He said it was important to not "lump" people who wanted to get their children vaccinated but could not for genuine reasons with those that were anti-vax.

'They think they know better'

Australian Medical Association (AMA) vice president Dr Stephen Parnis said it remained a source of "immense frustration" some parents chose not to vaccinate their children.

"There are people who in spite of overwhelming and controvertible evidence choose to believe myths which have no basis and fact," he told the ABC.

"These groups are resistant to science and think they know better than the medical and scientific communities."

Dr Parnis said keeping a decision to not vaccinate a child a secret was dangerous.

"There is a risk irrespective of whether they disclose it or not. But that risk could be amplified if they gain access to places where they shouldn't on the basis of not telling the truth — that might be a school," he said.

Dr Parnis said choosing not to hide the truth would hopefully trigger a person to consider why they chose not to vaccinate in the first place.

Herd immunity believers 'playing with fire'

The Edith Cowan University study highlights that many parents who do not vaccinate their children rely on herd immunity.

The concept is based on the belief that once immunisation rates reach between 90-95 per cent, unimmunised people are protected indirectly.

A National Health Performance Authority report on immunisation rates for children in 2012-13 showed immunisation rates for 1-year-olds was lower than 85 per cent in some areas.

The herd immunity theory is unreliable, according to the AMA.

"They are playing with fire if they continue to hold that belief ... and the evidence has shown their own children are the most susceptible," Dr Parnis said.

The study also indicated many parents believed a healthy diet and lifestyle was enough to protect against infectious diseases.

Dr Parnis said that alone could not reduce the risk of fighting an infectious disease.

"Those things are helping in terms of allowing for healthy growth and development," he said.

"But the fact of the matter is infectious diseases have varying methods of spread [and] are prevalent to varying factors like the time of year."

In addition to the well-known infectious diseases including whooping cough and rubella, Dr Parnis said people should be concerned about the spread of tetanus, diphtheria and the rota virus.

"We see those tragedies where an infant dies, Riley Hughes (who died from whopping cough) last year is the most prominent," he said.

"We are trying to protect newborn children in our community and it's fair to say we regard our newborn children as the most precious things we have."