Britons under the age of 40 will be offered their second Covid jab after eight weeks instead of 12, under new plans to get every adult fully vaccinated before winter.
Boris Johnson said the aim was for all adults to be inoculated by mid-September, when Covid rates are expected to rise and the NHS grapples with seasonal pressures.
Last month, the gap was shortened for older people in a bid to protect the most vulnerable amid the rise of the highly-infectious Indian variant.
Boris Johnson announced the change to the dosing strategy at tonight's press conference, where he set out plans for a post-lockdown England from July 19.
Ministers are also considering whether to roll out third vaccine doses for all over-50s, NHS staff, carers and patients with underlying health conditions this autumn.Insurance Loans Mortgage Attorney Credit Lawyer
An Oxford University study last week showed that antibody levels could be restored to their peak with the use of a 'booster' vaccine months after the second.
But whether or not this would improve on the already near-100 per cent protection against death that two doses provide is still unknown.
No10 is now wrestling with the moral dilemma of whether to run the booster vaccine programme or send the doses to developing countries where supplies are scarce.
Vaccinating children is another contentious strategy being considered by the Government, with some of its advisers warning that Covid itself is less dangerous to youngsters than a jab.
Originally, both AstraZeneca and Pfizer's vaccines were approved to be dished out in three-week intervals because that was the gap tested in the research trials.
But No10's scientists pushed the regimen back to 12 weeks to get wider protection in winter, when the second wave started to take off.
Studies since have shown that both jabs actually perform slightly better when the doses are spaced out for longer than a month.
Last week, it emerged that pop-up vaccine centres in London were ignoring official guidance and handing out second Covid vaccine doses to young people early.
The Government's top scientists say everyone under the age of 40 should wait at least eight weeks before getting their second dose and no more than 12.Insurance Loans Mortgage Attorney Credit Lawyer
It comes after over-40s had their second dose gap shortened last month in the face of the Indian variant.
Professor Anthony Harnden, who helped design the jabs priority list, said he wouldn't recommend getting the second dose of the AstraZeneca vaccine sooner than eight weeks after the first.
But he added the second dose of the Pfizer jab can be given from three to 12 weeks after the first dose.
Numerous studies have suggested that both the Pfizer and AstraZeneca jabs are more effective after a longer period between doses.
Second doses can be booked online with the NHS, or received at walk-in clinics.
There are around eight million adults in Britain who are yet to receive their first dose.
There were reports that walk-in vaccination centres at the Science Museum and Emirates Stadium were