The latest figures will disappoint public health specialists

In the second quarter of the year, 88% of two-year-olds had the injection - no change over the first three months.

However only 72% of one-and-a-half year olds had received the jab, suggesting that the number of children being immunised could fall further.

Last week a major study concluded that the MMR jab was not linked to autism.

Debate has raged over the safety of the combined vaccine, which some parents believe can cause autism.

The new figures, issued by ISD Scotland, which collects health service data, show that the uptake rate at 18 months (72.4%).

'Herd immunity'

This is described as low, compared to previous sets of statistics. The government's has set a target of 95%.

"The rate at 21 months... also appears relatively low at 82.2%, suggesting that the eventual rate at 24 months may be lower than the current rate of 88%," ISD Scotland's report said.

Ninety five per cent of children need to be immunised to ensure "herd immunity" and prevent outbreaks of measles, mumps or rubella.

Scotland's chief medical officer Dr Mac Armstrong said: "I am most encouraged by today's figures which show that take-up of all childhood vaccinations remains strong and I continue to encourage parents to immunise their children.

'Positive sign'

"I am also pleased to note that the uptake of the MMR vaccination remains at a higher level than in recent times.

"This is a positive sign and testament to the efforts of health professionals and parents in ensuring children are protected against the risks these diseases pose.

"MMR is the safest, most effective way to protect all children against the risks of measles, mumps and rubella."

Uptake rates at 12 months for diptheria, tetanus, polio and hib remain above 95%.