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.
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.
There were reports that walk-in vaccination centres at the Science Museum and Emirates Stadium were offering second doses to anyone who'd been jabbed