The number of Australian parents refusing to have their children vaccinated hardly changed from 2002 to 2013, say researchers.
Registered vaccination objection affecting children aged one to six years increased from 1.1 per cent in 2002 to two per cent in 2012 and no vaccinations were recorded for them.
But the increase was offset by a decrease in the number of partially vaccinated children whose parents had not recorded an official objection.
Vaccination coverage overall remained relatively high and stable.
Dr Frank Beard and colleagues from the National Centre for Immunisation Research and Surveillance and the University of Sydney examined trends in registered vaccination objection.
The study, in the Medical Journal of Australia, estimated the contribution of unregistered objection to incomplete vaccination among children in Australia.
"Most areas with high levels of recorded objection were in regional zones, with marked clustering in northern New South Wales and south-east Queensland," they said.
Objections were more common in affluent areas, while the number of children not fully vaccinated - but with no recorded objection - was higher among local socioeconomic areas.
This may be due to problems of access to health services, missed opportunities and logistical difficulties, suggest the authors.
Just over half of the 2.4 per cent of children with no vaccinations and no recorded objection were born overseas.
Most are likely to have been vaccinated but the information has not been recorded on the Australian Childhood Immunisation (ACIR) Register, suggest the authors.
"We recommend that primary care clinicians pay close attention to ensuring that the vaccination history of overseas-born children is correctly recorded in the ACIR," they said.
Data on registered objection is no longer collected, however, the ACIR collects data on children who are fully registered.
From January, philosophical and religious beliefs are no longer legally valid reasons for exemption from vaccination requirements for those receiving family assistance payments.
