A WA Health Department study into unvaccinated children has found the majority with no recorded immunisations are from overseas.
The report's authors were surprised by the findings as they expected "vaccine refusers" to account for most of the children not immunised in WA.
They believe there is a "gap" in the medical system that should be addressed.
Researchers contacted the parents of 853 Perth children who had no immunisation records with the Australian Childhood Immunisation Register.
Forty-six per cent of parents said they had moved from overseas and not provided their child's immunisation history to the ACIR, while 25 per cent of parents were vaccine refusers.
Just 1 per cent of those from overseas were considered to be "fully vaccinated", with most partially vaccinated.
Robyn Gibbs, who presented the report at this week's National Immunisation Conference in Melbourne, said the study showed that many migrant families were not being made aware they needed to register their child with ACIR.
"There's a gap when people register with Medicare - they're not being told that if they have children aged less than seven they need to have them registered," Dr Gibbs said. "We want to make people aware they need to do that because there are a lot of children moving to Australia from overseas and it may take them a while to catch up on vaccinations."
The report's authors have contacted the Commonwealth Health Department to recommend getting immunisation statements from families when they enrol with Medicare. "The results were surprising," Dr Gibbs said. "We thought most of those who didn't have immunisations were vaccine refusers."
It is estimated that about 3.3 per cent of WA children on the ACIR have no vaccinations.
Figures last month revealed about 4267 children, or 1.79 per cent of those under seven in WA, were classified as conscientious objectors or vaccine refusers.
The areas with the highest percentage of objectors were pinpointed at this week's conference by Dr Brynley Hull, from the National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases.
In WA, Mundaring had a 7.4 per cent rate of objectors, Bunbury 6.5 per cent and Fremantle 5.5 per cent.
Australian Medical Association president Michael Gannon said WA GPs were aware of the "hotspots".
"Not only are these the areas where there's less children enjoying the benefits of immunisation, but once you drop below 90 per cent for a lot of bacteria and viruses, you lose the protection of herd immunity and that's the real concern," he said.