People will be able to book their Covid boosters on Christmas Day as the NHS battles to give out around a million jabs a day to curb the threat of the Omicron variant.
Downing Street said medics would be working tirelessly to give all eligible adults their booster by New Year's Eve, after Boris Johnson brought the target forward by a month.
Mr Johnson delivered an address to the nation on Sunday night, where he announced a mass acceleration of jabs to tackle a "tidal wave" of Omicron cases.
There has been confusion over whether people will be guaranteed a jab by December 31, with NHS England saying everyone will have been offered the chance to book a booster.
On Sunday evening, the Prime Minister said people would be able to "get" their jab by that date.
No 10 confirmed that all eligible over-18s would be able to get their booster by the end of the year.
Asked to clarify, the PM's official spokesman said: "Everyone eligible aged over 18 in England will have the chance to get their booster before the New Year.
"Obviously there will be some individuals - for example if you've contracted Covid you need to wait 28 days or if you haven't had that requisite gap between your second dose for example then you might not be eligible.
"Those eligible will have their ability to get their booster before the New Year."
Asked if it was a target or an ambition, the spokesman insisted it was an "ambitious target" and applied to walk-ins and bookings.
The booster rollout will continue throughout the festive period.
Asked if their would be jabs over Christmas, the PM's spokesman said: "Vaccinations will continue to be offered throughout the Christmas period.
"If there is demand on Christmas Day, we are confident the NHS will find a way to match it."
Boosters are now available to everyone over 18, as long as their second dose was at least three months ago.
Over-30s can already book a booster online and from Wednesday this will be extended to over-18s.
The PM confirmed the first death with Omicron had occurred in the UK.
He told reporters: "Sadly, yes, Omicron is producing hospitalisations and sadly at least one patient has been confirmed to have died with Omicron.
"So I think the idea that this is somehow a milder version of the virus, I think that's something we need to set on one side and just recognise the sheer pace at which it accelerates through the population. So the best thing we can do is all get our boosters."
