Boris Johnson has said temporary vaccination centres are to pop up "like Christmas trees" as he set the challenge of offering all adults Covid-19 booster jabs in just 62 days.
All people aged 18 and over are to be offered a Covid-19 booster vaccine as part of efforts to tackle the spread of the new Omicron variant.
Health Secretary Sajid Javid said that the booster programme was being "put on steroids", but how long do you need to wait before having a third dose?
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When should the third jab be given?
Booster doses should be given no sooner than three months after people have had their second dose of an original vaccine - shaving three months off the current six-month wait, according to the JCVI.
The JCVI also said that severely immunosuppressed people should be offered a booster dose no sooner than three months after completing their primary course of three doses.
Who is eligible for a booster?
Vaccination experts advised on Monday that the booster programme should be extended to include all adults amid concerns about the Omicron variant - making 14 million more people eligible for a booster shot.
When will I get it?
The Prime Minister said that all adults would be offered a booster by the end of January.
But the head of the NHS warned that the campaign "can't happen overnight" and told people not to contact the NHS until they are called forward.
Like the initial vaccine programme, this programme will go down through the age groups in increments, this time by five-year gaps.
So how can I book my jab?
People who were already eligible will be prioritised.
An additional 6.9 million over-40s became eligible for a booster because the period between second jab and booster has been reduced to three months; people were previously asked to wait six months.
This group will be contacted first.
The NHS will then start calling forward the extra seven million people aged 18 to 39.
Where will I get my booster?
Mr Johnson said that temporary vaccination centres would "pop up like Christmas trees".
For instance, former health secretary Matt Hancock urged volunteers to come forward to help a mass vaccination clinic at Newmarket Racecourse in Suffolk, where it is hoped that 10,000 boosters will be delivered on Sunday.
Mobile vaccination units will also be used so people can "basically be vaccinated on their doorsteps", NHS chief executive Amanda Pritchard said.
Meanwhile, 1,500 community pharmacy sites will ramp up capacity - and be rewarded financially for doing so.
And hospital hubs will be expanded to vaccinate more patients, NHS and social care workers.
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