Health officials have warned of a “bumpy few months ahead” as they extended the Covid-19 booster programme to include healthy adults over the age of 40.

Ministers across the UK have accepted a recommendation from the Joint Committee on Vaccination and Immunisation (JCVI) that the booster programme should be extended to include people aged 40 to 49.

Second doses for 16 and 17-year-olds have also been approved after the JCVI said this group should be offered a second jab of the Pfizer/BioNTech jab 12 weeks after they received the first.

The JCVI said that the broadening of the booster campaign and the offer of a second jab to 16 and 17-year-olds will “help extend our protection into 2022”.

Prime Minister Boris Johnson urged people to get their booster to get the extra level of protection which will make “all the difference to winter, to Christmas”.

And England’s deputy chief medical officer Professor Jonathan Van-Tam said that everyone has a role to play in helping the UK have “as safe and disruption-free a winter as possible”.

Speaking on a visit to a medical centre in east London, Mr Johnson said: “What’s happening is if you can get your booster then your immunity goes right back up to 95%.

“So far we’ve got 75% of everybody over 70 getting a booster, there’s a huge number of people, but it’s that further 25% that will make all the difference to winter, to Christmas, to our plans going forward, because it’s that extra level of protection that we really need.

“So the message is: anybody over 70, come forward, get your booster; anybody over 50, come forward and get your booster now; in the next week or so, anybody over 40 as well, come forward and get your booster.”

Prof Van-Tam told a Downing Street press briefing: “I think for Christmas and the winter period, we can expect respiratory viruses to be around and we are particularly concerned that flu will come back and add to our problems, and it could be quite a bumpy few months ahead.

“But everyone has a key role to play in achieving as safe and disruption-free a winter as possible.

“Wear face coverings in crowded places if it is practical to do so, increase indoor ventilation whenever you can, make sure you are vaccinated and, like any medicine, make sure you finish the course.

“And when you are called for your booster please come forward at pace so that we as a whole UK can get on and finish this job.”

He added: “I believe that if the booster programme is successful, and with very high uptake, we can massively reduce the worry about hospitalisation and death due to Covid at Christmas, and for the rest of this winter for millions of people.”

Prof Van-Tam said that experts had seen a “signal” of waning immunity among those aged 40 to 49.

“While the vaccines have fundamentally changed the course of the pandemic in the UK, and the high uptake of the initial programme has saved countless lives and helped restore our freedoms in an unprecedented way, it is also clear that protection will wane over time after the first two doses of a primary course – that is especially so in older adults and those with risk conditions,” he said.

“The waning signal, while smaller, is also beginning to show in the 40-49s and without boosting I would not expect it to be static, I would expect it to increase.”

It comes as a new study highlighted how boosters can significantly increase people’s protection against getting a symptomatic case of Covid-19.

Two weeks after getting their booster, adults over 50 had at least 93% reduced risk of getting a symptomatic case of Covid-19, according to a study from the UK Health Security Agency (UKSHA).

Protection against more severe disease and death is expected to be even higher.

Professor Wei Shen Lim, chair of Covid-19 immunisation for the JCVI, said: “The booster dose markedly strengthens existing protection and will extend the duration of that protection against serious disease.

“We therefore urge people who are eligible for a booster to step forward and have your booster and maximise your protection.”

He added: “Booster vaccine doses in more vulnerable adults, and second vaccine doses in 16 to 17-year-olds, are important ways to increase our protection against Covid-19 infection and severe disease.

“These vaccinations will also help extend our protection into 2022.”

Prof Van-Tam said that the nation was in a period of “near-term danger” but he hoped for “calmer waters” by spring.

He told the briefing: “I regard it as still a time of great delicacy and quite a bit of near-term danger.

“Do I personally frame that if our booster programme goes well and vaccine uptake remains high, that we will be in a much set of calmer waters by the middle of spring? then I think I do. But this virus is unpredictable.

“But I do see, once the spring gets here, hopefully some calmer waters ahead.”

He also made a plea for unvaccinated people and those who had only had one vaccine to come forward to ensure they are protected.

The NHS has been asked to prepare to offer those eligible a booster vaccine as soon as possible.

So far, some 12.6 million people have had a third Covid-19 jab.

The JCVI said people should be offered the Pfizer or Moderna jab as a booster, irrespective of which vaccine they had initially.

The booster will be offered sis months after the second vaccine was given, with people able to book their appointment after five months.

Health and Social Care Secretary Sajid Javid said in a statement: “Our Covid-19 vaccination rollout has been a phenomenal success, saving countless lives, reducing pressure on the NHS and helping us stop the spread of the virus.

“We are expanding the programme even further and today I have accepted the advice from the independent experts at the JCVI to extend the additional offer of a booster jab to people aged 40 and over and offer a second dose of a vaccine to all young people aged 16 to 17 as part of the primary vaccination schedule.

“All four parts of the UK intend to follow the JCVI’s advice.

“I have asked the NHS to prepare to offer those eligible a vaccine as soon as possible.”

He added: “The JCVI will keep under review whether the booster programme should be extended to all people under the age of 40 and I look forward to receiving their advice in due course.”

Prof Lim said that it was not yet clear whether under-40s would need a booster.

He told the Downing Street briefing: “It may well be that adults who are under 40 years might require a booster dose or a third dose at some point, we don’t know whether that is definitely the case yet.

“We are looking very closely at the data all the time and should there be sufficient signal to warrant a third dose, so a booster dose for this age group, then certainly we will announce that and advise that accordingly.”

The Medicines and Healthcare products Regulatory Agency (MHRA) said the announcement “strengthens our ability to ensure people are protected against Covid-19 and saves lives”.

Earlier on Monday, Government minister Oliver Dowden said it was up to the public whether new controls would need to be imposed over the winter months.

Mr Dowden said the vaccination programme offers the best assurance that further Covid-19 restrictions will not be needed over Christmas.

The Conservative Party chairman told Sky News: “It is in our hands. If you get the booster when the call comes that is the biggest wall of defence that we have against Covid.”