The Joint Committee on Vaccination and Immunisation (JCVI) said all adults over the age of 40 should be offered a booster, six months after their second dose.
It has also said that 16 and 17-year-olds should come forward for a second dose of the Pfizer/BioNTech jab – which should be given at least 12 weeks after 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”.
It comes as ministers urged people to get boosters when called in a bid to save Christmas.
Government minister Oliver Dowden said it was up to the public whether new controls would need to be imposed.
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.
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: “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.
“If you are eligible, please make sure to have these vaccines and keep yourselves protected as we head into winter.”
Dr June Raine, chief executive of the MHRA, added: “We welcome today’s announcement by the JCVI, on the extension of the booster campaign to 40-49 year olds.
“This further strengthens our ability to ensure people are protected against Covid-19 and saves lives.
“Our safety monitoring to date shows that Covid-19 vaccines continue to have a positive safety profile for the majority of people. The vast majority of reactions which are reported relate to expected side-effects such as injection site reactions and flu-like symptoms, as was seen in our initial assessment.
“Our proactive monitoring of the safety of booster doses does not raise any new concerns.
“People can be reassured that when we gave approval for the Pfizer vaccine for those 16 years and over in December 2020, we had thoroughly reviewed all the clinical trial data.
“We have continued to carefully scrutinise all the data we have available to us and our robust surveillance programme includes monitoring all suspected reactions for adolescents as well as adults.
“We ensure all suspected reports are carefully followed up. The Expert Working Group of the Commission on Human Medicines has confirmed that reports of suspected myocarditis (heart inflammation) following Covid-19 vaccines are extremely rare and that the balance of risks and benefits overall remains favourable.”