The booster vaccine rollout was introduced as a way to improve the protection offered by the first and second doses of the Covid-19 vaccines.
Originally available for the elderly and clinically vulnerable - and in attempt to curb Covid cases this winter - the booster jab is now set to pick up pace.
Prime Minister Boris Johnson stressed on November 15 that getting the Covid booster jab was essential in protecting the UK from the rising cases seen in Europe - and now with the confirmation of the omicron variant reaching the UK, the booster vaccine rollout appears more necessary than ever.
Below, we have answered the key questions about the booster vaccine, how to register for one and what getting your top-up jab means.
Who is now eligible for the booster?
The minimum wait time before having a Covid booster jab will be halved from six months to three in a bid to speed up the programme to limit the spread of the new omicron variant.
This will mean that the vast majority of people over the age of 18 will technically be eligible. However, health officials have stressed that they will still call people forward in age order, saying people should wait to be contacted.
Until now, only those over the age of 40, and those in priority groups were eligible - and only if it was six months since their second jab.
How long do I have to wait after my second jab to get the booster?
The new advice says boosters must be a minimum of three months after the second jab. But as the rollout will work down through age groups, most of those being offered boosters in the next few weeks are likely to have waited at least five months.
Prime Minister Boris Johnson announced in a briefing on November 30 that the target the government has set is to offer a booster to everyone eligible by the end of January, and the NHS will be working through those eligible by five year age bands.
Asked whether the target of the end of January is really realistic, considering it would involve giving some three million people a week a shot, NHS England chief executive Amanda Pritchard said: "It is our clear intention to ensure everyone who is eligible has a chance to book that booster by the end of January. There's no maximum to the number of jabs we aspire to give week on week, but we do need to recognise this will build up."
Where can I get my booster?
Once the NHS has invited you for your vaccine, you should be able to book a slot online at mass vaccination centres, hospitals, pharmacies and some GP practices. Health officials had previously said extra hospital sites would be opened, with others open for extended hours.
At the Downing Street briefing, Amanda Pritchard confirmed that there are now 3,000 vaccination sites across the country - more than double the number at the start of the year - while pop up clinics will make shots even more accessible. You can find your nearest walk-in clinic offering booster jabs using the NHS finder.
She also said the NHS are recruiting for 10,000 paid vaccinating roles and also volunteers as the vaccination rollout expands again.
Which vaccine will I get?
The vast majority of people will be offered Pfizer BionTech or Moderna. A small number of people who are unable to receive this type of jab will be offered AstraZeneca. As with the first and second doses of the Covid-19 vaccine, you won't be able to choose which vaccine you will get so there's a chance you may receive a different brand of booster. A recent study by Oxford University found that mixing and matching vaccines can induce more immunity than having the same brand of jab.
What level of immunity does the booster give?
Booster doses have been found to provide 93 per cent protection against severe disease.
At the moment, it isn’t known how well the jabs work against the new omicron variant, and there may be a level of “mismatch” between vaccine and variant. However, scientists believe that the jabs are still likely to prevent severe disease.
How can I book a booster vaccine?
During his press briefing on November 30, the Prime Minister said that people should not try to book their vaccination until they are invited to come forward by the NHS, but added: "We are going to throw everything at it, to ensure that everyone eligible for that booster will be vaccinated within two months".
He said that there will be temporary vaccination centres "popping up like Christmas trees", with the military, pharmacies and GPs deployed in an attempt to hit the daily vaccination rate seen earlier this year.
This was echoed by Amanda Pritchard who urged: "If you are not already eligible, please do not contact the NHS," stressing that those eligible will be told when they can access shots.