Unjabbed Britons have a two-week window to get a Covid booster if they want to have maximum protection from the virus on Christmas Day.
The NHS has issued a plea to the roughly 7million — or three in 10 — eligible people who have yet to have the crucial third dose.
Real-world UK data shows protection against getting sick with Covid rises to more than 90 per cent two weeks after the injection. Immunity against hospitalisation and death is even higher.
It means that getting a booster by December 11 will give people 'very high protection against Covid by Christmas day', officials said.
Boosters are being offered to everyone over 40, so long as it has been six months since their second dose. But people can book their appointment at the five-month mark.
Figures show 23million people were double-vaccinated against Covid by May 25, roughly six months ago.
Currently 16 million boosters have been administered, suggesting 7million (30 per cent) have still to come forward.
The UK is hoping for a relatively normal Christmas this year after surging Covid cases in the last few weeks of 2020 prompted last-minute lockdown curbs.
The fresh plea from the NHS and Government has been backed by 16 health charities representing people with health conditions that make them more vulnerable to the virus, and their carers.
The coalition between the groups comes as figures show a total of just over 16million people got their Covid booster in the UK by yesterday.
This leaves about 7million people eligible for the third dose of the Covid vaccine who are yet to come forward.
The charities represent people who are especially vulnerable to a potential Covid or flu infection, such as those with heart conditions or diabetes, or people with a compromised immune system such as those undergoing cancer treatment.
