Following a meeting last month, the Joint Committee on Vaccination and Immunisation (JCVI) said it required further assessment on the impact of such an extension to the UK's national programme before it could recommend vaccinating under 17s against flu.
The decision followed a request from health secretary Andrew Lansley to look at whether the flu vaccination programme should be extended.
The JCVI said vaccinating older people and all those in the clinical risk group should remain the priority.
A preliminary study by the UK's Health Protection Agency had suggested it might be cost effective to vaccinate healthy children to reduce flu transmission.
But the JCVI said a further assessment was needed into the impact on GP practices and schools of vaccinating healthy children.
The UK's director of immunisation Professor David Salisbury said: 'Extending the vaccination programme to all healthy children under 17 would be a huge undertaking, increasing the number of people who get the vaccine, so it is important that we get this decision absolutely right.'
He added that a 'key consideration' would be the availability of vaccine suitable for this age-group, which would likely be in the form of nose drops.
'But we need to understand from vaccine manufacturers how and when they would be able to produce the vaccine in the quantities we need.'
Vaccination rates across the UK remain relatively low. In England, although 54.8% of over 65s have had the jab already, just 32.2% of at-risk people and 13.5% of pregnant women have been vaccinated.
Click here to explore the current flu situation across all four UK countries in our interactive guide