The JCVI has also announced that 16- and 17-year-olds will be offered second doses. The rollout of jabs to this group began in August.
Officials said that they will be given a gap of at least 12 weeks between doses, to maximise the efficacy of the dose, and reduce the risk of side effects.
Their research found 9 per million cases of myocarditis – a rare type of heart inflammation- in those under the age of 18 who received vaccinations.
Most people in this age group have only received one dose, as it is so far not recommended for healthy children under the age of 17.
The rate was 21 per million for those aged 18 to 29 for the first dose, and 20 per million for second dose.
Dr June Raine, chief executive of the Medicines and Healthcare Products Regulatory Agency said: “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. “We also welcome the recommendation for 16-17 year-olds to come forward and have a second dose of the Pfizer/BioNTech vaccine.
“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.”
Health officials said results from the first UK real world study by the UK Health Security Agency (UKHSA) show significantly increased protection against symptomatic disease from a booster dose of the Pfizer-BioNTech vaccine in those aged 50 years and older.
“These findings show that two weeks after receiving a booster dose, protection against symptomatic infection in adults aged 50 years and over was 93.1 per cent in those with AstraZeneca as their primary course and 94.0 per cent for Pfizer-BioNTech.
After a primary course of AstraZeneca and Pfizer-BioNTech vaccines, effectiveness against symptomatic disease appears to wear off with time. Scientists said that overall, vaccine effectiveness against severe outcomes such as hospital admission remains high for several months after completing the primary course, but greater waning has been seen in older adults and those with underlying medical conditions compared to young, healthy adults.
Dr Mary Ramsay, Head of Immunisation at the UK Health Security Agency, said: “Our findings demonstrate the protection provided by the booster dose against symptomatic infection in those at highest risk from developing severe COVID-19. We know that in older age groups, protection from the first two vaccines is beginning to wear off, leaving millions that need extra protection as we head into winter.
“That is why it is critical that you come forward for your booster as soon as you become eligible so we can drive down hospitalisations and deaths over the winter.”