Shadow health secretary Andrew Lansley said: ‘The drop in the number of new swine flu cases during half-term appears to point to the role that schools play in spreading the H1N1 virus.

‘This is further evidence that we need to begin planning a school and college-based vaccination programme immediately. It may also be more beneficial if that programme is prioritised in areas where the virus has had less impact so far. The government needs to press on with decisions and preparations without delay.'

England's chief medical officer Sir Liam Donaldson said: ‘We are not holding back because we don't have enough vaccine available. We will want to plan in advance and get everybody ready when we do decide to go ahead. We're just having a final look at the evidence, but no decision has been taken yet.'