Speaking at a DoH briefing in central London last week, Sir Liam said that research was being done to see if the seasonal flu jabs could offer protection.
'Swine flu is an H1N1 virus which is a subtype of our seasonal flu.
'Although it is not the seasonal strain, it may be an older H1N1 strain that may have been around in the past.
'The immune systems of older people might have some memory of the H1N1 virus that could offer cross-protection,' he added.
The human part of the A(H1N1) virus may not be novel, but we do not know that yet, Sir Liam said.
A spokeswoman for the DoH said: 'It is thought possible, though by no means certain, that some current seasonal influenza vaccine might boost pre-existing immunity, thereby providing some degree of indirect protection. This is being looked at urgently by experts.'
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