It said 13 per cent of parents delayed immunising at six weeks, 19 per cent at three months and 27 per cent at five months. Seven per cent did not immunise at six weeks or three months and 11 per cent at five months.
The study, of 6822 women and 4404 of their partners, also found "encouraging" information had no effect on when they chose to immunise, and more than half, 56 per cent, did not receive any information at all before birth.
Auckland mother of two Masako Morita said that although her Plunket nurse seemed to favour immunisation, she had already made up her mind to immunise. Both her daughters Lea, 5 and Maya, 9, were immunised on time.
"I come from Japan, I don't know anybody who doesn't immunise and don't know anyone who has had any negative experiences with it."
While most discouraging information came from friends, books, magazines, newspapers, family and the internet, Dr Grant said it was worrying that healthcare workers were identified as sources of 16 per cent of discouraging information.
He added that the benefits of immunising outweighed the relatively minor risk vaccines posed. Numerous scientific studies had also debunked myths linking vaccines to diseases such as autism and Crohn's.
"If vaccinations are delayed then you have a five-times-increased risk of getting hospitalised with whooping cough," Dr Grant said.
"Babies are particularly vulnerable to complications from serious diseases that can be stopped with a simple vaccine.
"In the last whooping cough epidemic [2012 to 2013] we had the equivalent of a baby in our intensive care unit with whooping cough every day for a thousand days."
He said that once in intensive care there was a one-in-six chance of the baby dying or being left with permanent lung or brain damage.
Last year, a coroner's report into the death of a 6-week-old Christchurch baby from whooping cough highlighted the need for widespread vaccination. Alaya-Reign Faalilo Ma'anaima died in Christchurch Hospital in 2012 after a bout with the disease led to widespread organ failure.
Dr Grant said another epidemic was likely as soon as late next year.
"Immunisation is one of the most effective and cost-efficient ways to prevent disease and improve health."
This year, Northland GP Lance O'Sullivan, New Zealander of the Year 2014, advocated for New Zealand to follow Australia's lead in cutting child welfare payments to families who did not vaccinate their children.
He said it was not welfare-bashing but a "proactive idea to ensure vulnerable children are protected".
Hot topics at conference
Ongoing issues of vaccine hesitancy, the availability and tone of immunisation information and new research findings are some of the hot topics at the annual Immunisation Conference this week in Hamilton.
Epidemiologist Dr Sarah Radke highlighted the importance of children and pregnant mothers getting booster shots against whooping cough.
Her study confirmed the current three-dose vaccine course delivered in infancy protected a child up till 4.
Booster shots were available at 4 and 11, and since 2013 had been funded for pregnant mothers.
However, Linda Hill, who authored another study being presented at the conference, said not all mothers were aware of its availability.
Other findings being presented at the conference will show how the rotavirus and influenza vaccines have reduced levels of the disease.
Dr Mark Jacobs, director, Communicable Diseases from the WHO's Western Pacific Regional Office, will also provide a progress update on the region's vaccination programme goals.
For more information visit immune.org.nz
