The proportion of two-year-old children in England having the MMR vaccine has fallen, according to NHS statistics.
In 2014-15, 92.3% of children had the jab to protect them from measles, mumps and rubella.
The Health and Social Care Information Centre said the figure was 92.7% in the previous year - which was the highest level of coverage ever achieved.
Some parts of the country had less than 80% of children immunised against the infections.
The target rate is 95%, which is enough to prevent the diseases spreading in a community.
A completely discredited health scare linking the MMR jab to autism led to immunisation rates plummeting a decade ago.
Between 1996 and 2004, vaccination rates fell from around 92% to 80%.
The dramatic fall led to an "unvaccinated generation" susceptible to the infections which culminated in the biggest measles outbreak in England for nearly two decades when nearly 2,000 cases were reported in 2012.
Coverage had been increasing every year since 2007-08 and eventually reached record levels before the latest dip in vaccination rates.
Dr Mary Ramsay, the head of immunisation at Public Health England, said it was "pleasing" that MMR coverage was still high.
She added: "We urge all parents to check that their children are up-to-date with their vaccinations and to contact their GP as soon as possible if they are unsure so that no child misses out."
However, the overall figures hide huge variation.
Parts of the West Midlands and the north of England were immunising more than 95% of children.
While in some London boroughs and the south east the figure was below 80%.
Scotland, Wales and Northern Ireland all have figures above 95%.
Measles is a highly contagious disease characterised by a high fever and a rash. In one in 15 cases it can lead to severe complications, such as pneumonia and inflammation of the brain, and can be fatal.
Dr David Elliman, an immunisation expert for the Royal College of Paediatrics and Child Health, said: "It is disappointing that uptake of NHS immunisations have not continued to rise, however the falls are very small.
"This could be read as children not receiving the vaccination or alternatively, it could be a lack of data collection linked to considerable pressures on staff working in the NHS.
"In view of the considerable upheaval that the NHS is going through, it's a credit to staff that we haven't seen bigger falls in uptake."