It's after concerns over very rare blood clots.
All under-40s are to be offered an alternative to the Oxford/AstraZeneca Covid vaccine in a precautionary move.
The Joint Committee on Vaccination and Immunisation (JCVI) has raised the age threshold after the UK’s medicines regulator reported new figures on blood clots last week despite saying that there is an “extremely small risk” of that happening.
The policy of offering an alternative vaccine previously only applied to the under-30s.
Professor Wei Shen Lim, Covid-19 chairman for JCVI, said: “We have continued to assess the benefit/risk balance of Covid-19 vaccines in light of UK infection rates and the latest information from the MHRA on the extremely rare event of blood clots and low platelet counts following vaccination.
“As Covid-19 rates continue to come under control, we are advising that adults aged 18 to 39 years with no underlying health conditions are offered an alternative to the Oxford/AstraZeneca vaccine, if available and if it does not cause delays in having the vaccine.”
The change comes despite the JCVI and the Medicines and Healthcare products Regulatory Agency (MHRA) saying there are no fresh safety concerns.
The JCVI, which advises UK health departments on immunisation, added that the risk of serious illness with Covid-19 also drops for younger people as infection rates fall across the country.
Up to April 28, the MHRA had received 242 reports of blood clots accompanied by low blood platelet count in the UK, all in people who had AstraZeneca, out of around 28.5 million doses given.
These clots occurred in 141 women and 100 men aged from 18 to 93, and the overall case death rate was 20%, with 49 deaths. Six cases have been reported after a second dose of the vaccine.
A particular type of brain blood clot – cerebral venous sinus thrombosis (CVST) – was reported in 93 cases (with an average age of 47), and 149 had other major thromboembolic events (average age 55) accompanied by low blood platelet count.
The MHRA and JCVI have both said that the benefits of the AstraZeneca vaccine continue to “outweigh the risks for the vast majority of adults”.
Professor Jonathan Van-Tam, deputy chief medical officer for England, said it is important that the vaccine rollout continues at a good pace, to control coronavirus and minimise the impact of any increase in cases.
During a televised briefing on Friday, he said: “The point has been emphasised several times already this morning about maintaining the pace and the volume of the vaccine rollout in order to control the disease in our country, long term, and to minimise the impact of any upsurge in cases potentially associated with a third wave.
“I can’t overemphasise that enough. I can say to you on top that on current plans, our vaccine supply schedule will support the change offered by the JCVI (Joint Committee on Vaccination and Immunisation) without limiting the speed and scale of the vaccine rollout.
“I do expect that we are still on target to offer a first dose to all adults by the end of July.”