The Government has warned of Christmas Covid restrictions as it urges people to take up booster jabs amid waning resistance.

Health Secretary Sajid Javid said the push to get people to have the top-up was a “national mission”.

Meanwhile, the chief medical adviser at the UK Health Security Agency said the number of deaths among the vaccinated population is on the rise as protection weakens.

Ministers are also considering changing the rules, so those who have not received the top-up jab may face travel restrictions.

Mr Javid said younger relatives should urge eligible parents and grandparents to take up the offer of a booster and the flu vaccine, saying if “we all come together and play our part” then the country can “avoid a return to restrictions and enjoy Christmas”.

He said: “We know immunity begins to wane after six months, especially for the elderly and the vulnerable, and booster vaccines will top up their protection to keep people safe over the winter.

“I strongly urge everybody who is eligible for a Covid-19 booster or flu vaccine to take up the offer as soon as you can.

“And if you haven’t yet had your first and second vaccines, it is not too late, the NHS will always be there to welcome you with open arms.”

The third jab could also become a requirement to avoid travel restrictions in a move which may further drive take-up.

Official guidance was updated earlier this month to say the Government “is reviewing the implications and requirements of boosters for international travel certification” and “looking at whether and how booster vaccinations could be included in the NHS Covid Pass for travel”.

But the Mail on Sunday reported that officials are divided over how soon to implement the measures and are discussing a grace period to allow people to continue to travel without quarantine if they have sought a booster six months after their second jab but have not yet been offered an appointment.

The chief medical adviser at the UK Health Security Agency, Dr Susan Hopkins, said elderly and vulnerable people who are double vaccinated have started dying due to the Covid-19 vaccine’s efficacy waning.

She said: “We’re still seeing deaths in mainly the unvaccinated population, but increasingly, because of immune waning effects, there are deaths in the vaccinated group as well.

“The people who are dying are the same people who have died all the way through.

“It is particularly the older age groups, so the over-70s in particular, but also those who are clinically vulnerable, extremely vulnerable, and have underlying medical conditions.”

People over 50 and those most at risk from Covid-19 are currently eligible for a booster six months after their second jab.

NHS figures from Sunday show that more than seven in 10 people aged 80 and over have had a booster while almost three in five people aged 50 and over have had one.

Ten million people had received the booster by Sunday, but about 30% of over-80s and 40% of over-50s in England are yet to receive a booster, the Department of Health and Social Care said.

Three million more people in England are being invited to have their coronavirus booster jabs next week, after Saturday saw a record day, with more than 371,000 people receiving one.