By Nick Triggle
Health reporter, BBC News
Swine flu cases are rising at a slower level
All schoolchildren and college students should be vaccinated against swine flu, the Tories say.
The party urged the government to act as evidence suggested the young were more likely to get the virus - and to develop complications.
Vaccination is already under way in the UK with those with health problems and pregnant women getting the jab first.
But the Tories said NHS chiefs should prepare to extend it to under-24s now. A decision is expected soon.
The call comes as the death toll has reached 154 in the UK, although latest figures show little increase in the number of weekly new swine flu cases.
In England, new infections rose by only 6,000 to an estimated 84,000 - still some way short of the summer peak.
In Scotland there was a small fall to just over 17,000.
Levels in Wales and Northern Ireland were much lower.
Nonetheless, Sir Liam Donaldson, the government's chief medical officer, said he was worried about the number of people ending up in hospital.
He said there had been a "snowballing" of critical care cases in particular.
At the start of the pandemic in the UK just one in 10 hospital patients ended up in intensive care, but that rate is now one in five.
And Sir Liam Donaldson was quick to dismiss suggestions that the tailing off in new cases could signal the end of the winter peak.
"This could be a half-term effect - we can't be sure. We have to wait and see. I am not reading too much into it."
He pointed out that the US saw a similar pattern a few weeks ago since when the number of cases has surged.
He also reiterated his position that the vaccine programme would be extended - but government experts were still weighing up the best way to do that.
More than 14m people will be vaccinated by the middle of December from the priority groups already identified.
But the Tories said it was essential to put plans in place for young people so that immunisations could start as soon as the first wave was completed.
The hospitalisation rate of the under 5s is twice as high as any other age group and children in general are more likely to spread the virus because of the way they play and interact.
Shadow health secretary Andrew Lansley said with such compelling data available the UK should follow the lead of the US and vaccinate the under 24 age group.
"A school-based programme needs preparation and needs to be coordinated with vaccine availability.
"I urge the government to make the decision and put the plan in place."
A Department of Health spokesman said vaccination was driven by evidence.
"The Chief Medical Officer has already announced that the vaccine programme will be extended.
"Never before have we been in such a fortunate position to have vaccine so early in a pandemic - but we don't have enough to protect everyone at once, so the most vulnerable people must come first."