Opposition Leader Tony Abbott says child immunisation rates have fallen under the Labor government.

"[During the Howard government] vaccination rates went back up over 90 per cent, a great achievement of a Coalition government," Mr Abbott told the Ten network's Meet the Press on August 18.

"Now they are dropping back again," he said.

"I think it is important to do what we reasonably can to get them up again... I just wish that this Government hadn't presided over a reduction in vaccination rates."

Later that day, Prime Minister Kevin Rudd said Mr Abbott had his facts wrong.

"When we came to office, the immunisation rate for five-year-olds was standing at 83 per cent," Mr Rudd said during a press conference at Westmead Hospital in Sydney's west.

"Through the excellent efforts of Tanya Plibersek, the Health Minister, and our colleagues across the states, we have lifted that to 90 per cent and reinforced that work through our Medicare Local teams, who have immunisation officers at work as well," he said.

"So Mr Abbott, if you're going to enter the debate on immunisation, get your facts right.

"We have increased it from 83 to 90 per cent - we want to get it from 90 per cent to as close to 100 per cent as possible."

ABC Fact Check asked the federal Department of Health and Ageing for the percentages of children immunised each year from 2007 to 2013.

It provided figures for one-, two- and five-year-olds for each financial year.

The statistics show that immunisation rates under the Labor government have remained stable for the youngest cohorts.

The rate for one-year-olds has risen slightly from 91.2 per cent in 2007-08 to 91.3 per cent in 2012-13. The rate for two-year-olds has fallen slightly from 92.7 per cent to 92.4 per cent.

The immunisation rate for five-year-olds has risen from a base of 79.4 per cent in 2007-08 to 91.5 per cent in 2012-13.

In the six months to March 2008 - the commencement of the Rudd government - the rate for five-year-olds was 82.9 per cent.

That confirms Mr Rudd's claim that under Labor the five-year-old rate has risen from 83 per cent to 90 per cent.

ABC Fact Check asked Mr Abbott's office why he said rates had fallen under Labor.

A spokesman for Mr Abbott said the Opposition Leader was referring to quarterly statistics published by Medicare.

"Immunisation rates for children at 12 months have fallen from 91.3 per cent in 2007 to 90.4 per cent in March 2013 and for children at 24 months from 92.7 per cent in 2007 to 92.1 per cent," he said.

Mr Abbott's spokesman said the rate for five-year-olds had been affected by government changes.

"Kevin Rudd's reference related to rates for five-year-olds," he said.

"In December 2007, the Australian Childhood Immunisation Register changed the benchmark for an immunisation cohort from six years to five years, hence there was a period of catch up for five years olds.

"This means there was a lag in time until all five-year-olds were vaccinated to what was previously measured at six years of age."

The Australian Childhood Immunisation Register is maintained by Medicare, which is administered through the Department of Human Services.

When ABC Fact Check asked for their data, the Department of Human Services passed the inquiry to the Department of Health, which provided Medicare with the information used in its quarterly chart.

The Department of Health also provided the annual figures used by ABC Fact Check.

ABC Fact Check considers the annual immunisation figures are more reliable than the quarterly figures, as quarterly figures vary more due to patterns in children's birthdays.

In any case, Mr Abbott framed his comments by reference to the Coalition achieving a rise in rates above 90 per cent.

Rates for one- and two-year-olds have been consistently above 90 per cent throughout Labor's term in office and the rate for five-year-olds has been above that level since 2012.

But while the national numbers are consistent with Labor's position, there are hot spots around Australia where rates are either significantly lower, or higher, than the average.

Why does the immunisation rate matter?

Rates of immunisation matter because of a concept called "herd immunity".

If vaccination rates fall below a certain point it becomes harder to stop a major outbreak, one that will potentially infect people who have had a jab as well as those who have not.

For some illnesses in some areas of the country herd immunity is dangerously low.

The Herd Immunity Threshold for measles is somewhere between 83 and 94 per cent. For whooping cough it is between 92 and 94 per cent.

Nationally, Australia sits right at 94 per cent for measles and 92 per cent for whooping cough.

In parts of Australia - including the Blue Mountains, the Sunshine Coast, inner Brisbane, inner Sydney, Adelaide and Darwin - the rates have fallen below 85 per cent for five-year-olds.

On the far north coast of New South Wales, the rates are under 85 per cent in all three age groups.

The verdict

Given the overall vaccination rates across all three age groups over the period of the Labor governments has either remained stable or increased, Mr Abbott's claim that "this Government (has) presided over a reduction in vaccination rates" is wrong.

Sources

Editor's note: This fact check has been updated to incorporate comments from Mr Abbott's office.