Participant in the swine flu vaccine trial, Suzanne Verster, is given her dose
A swine flu vaccination campaign will be launched in the autumn, but only certain at risk groups, including pregnant women, will be given the jab.
Those with underlying health conditions up to the age of 65 have been identified as the first priority in the UK followed by pregnant women.
Health and social care workers will also get the jab, meaning about 14m people will be immunised by December.
The government has yet to decide whether everyone should be given it.
There are contracts in place for 132m doses of the jab - enough for the whole population as people will require two shots.
Nearly 55m doses should be available by the end of the year, compared to the 15m ordered annually for seasonal flu.
Sir Liam Donaldson: Government will concentrate on 'vulnerable' first
Chief Medical Officer Sir Liam Donaldson said the vaccine was going through similar safety testing as the seasonal flu vaccine.
He added: "We have a real chance to save lives if we can get the vaccine in place.
"We are putting up a real fight against this virus."
The vaccine programme is due to roll out as follows if it is granted approval by European regulators in late September or early October as expected:
• In October, those aged six months to 65-years-old in conventional at-risk groups for normal seasonal flu, such as those with diabetes or heart disease, will be vaccinated.
• This will be followed by all pregnant women, subject to licensing arrangements and better information on when in the pregnancy the vaccine should be given.
• People living in households with patients with suppressed immune systems and those over 65 in conventional at-risk groups will then be eligible.
• Front-line health and social care workers will then be vaccinated.
• By the middle of winter, the government hopes to have enough evidence to decide whether the campaign should be extended to healthy people.
Many people had expected children to be among the first wave of priority groups.
But experts ruled this out because while they have been the worst hit in terms of the number of cases it is mainly those with underlying health conditions that have developed complications.
Sir Liam said: "We have to protect the most vulnerable first."
Dr Steve Field, chairman of the Royal College of GPs, told BBC Radio 5 live that medical staff had a duty to explain their reasoning to the public and allay their fears.
He added: "The patients do trust us but we have to be honest with them. This isn't a paternalistic thing."
A total of 300,000 doses of the vaccine will be delivered this month by the two manufacturers contracted by the government.
But this will increase dramatically in the coming months, although the 54.6m prediction is still less than expected as one of the firms, Baxter, has had trouble developing enough virus to make the vaccine.
It is envisaged those who are also eligible for the seasonal flu vaccine will get both jabs in one go.
However, the UK health departments are still in discussions with the British Medical Association about how GPs will administer the programme.
The announcement about the vaccine programme comes as the number of newly diagnosed with swine flu continues to fall.
There was an estimated 25,000 new cases in England in the last week compared with 30,000 the previous one.
In Scotland there were more than 3,000 cases and in Wales more than 1,600. Northern Ireland has seen less than 100 cases since the outbreak began.
In total, 49 people across the UK have died with swine flu - nine in the past week.
Sir Liam also announced plans to scale down the National Pandemic Flu Service for England, from around 1,600 call centre agents at its launch to between 200 and 600 from 23 August.
New cases are expected to continue falling over the summer with a surge in the autumn after children go back to school.
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