The Prime Minister said the accelerated rollout would help protect the most vulnerable sooner and enable the easing of some restrictions.
Adults aged 50 and over – as well as those with underlying health conditions which put them at higher risk – will be offered a vaccine by April 15 under the expedited plans.
By July 31, all adults should have been offered a jab – though the order of priority for those under 50 has yet to be outlined by the Joint Committee on Vaccination and Immunisation (JCVI).
Ministers had set a target to offer vaccines to all adults by September, with an aim to reach all those aged 50 and over in the first nine JCVI priority groups by May.
The new targets will be seen as a sign of increasing confidence within Government that the vaccine supply will remain steady over the coming months.
The Government met its ambition to offer jabs to all those in the top four priority groups – adults aged 70 and over, frontline health and social care workers and the most clinically vulnerable – by February 15.
More than 16.8 million people have now received their first dose of a vaccine at one of the 1,500 vaccination sites across the country, and almost 600,000 have received their second.
The accelerated rollout will fuel calls for coronavirus restrictions to be eased sooner, but Mr Johnson insisted the route out of lockdown would be “cautious and phased”.
The Prime Minister will spend the weekend finalising his road map for relaxing the stringent measures before announcing the plans to MPs on Monday.
He said: “Hitting 15 million vaccinations was a significant milestone – but there will be no let up, and I want to see the rollout go further and faster in the coming weeks.
“We will now aim to offer a jab to every adult by the end of July, helping us protect the most vulnerable sooner, and take further steps to ease some of the restrictions in place.
“But there should be no doubt – the route out of lockdown will be cautious and phased, as we all continue to protect ourselves and those around us.”
Downing Street said the JCVI would publish its priority list for the second phase of the vaccine programme in due course, amid calls for teachers and other frontline workers to be prioritised.
Shadow health secretary Jonathan Ashworth said: “The success so far of the vaccination rollout shows the true value of our incredible health service, and my thanks goes out to our NHS staff, armed forces and volunteers working hard to make this happen.
“Ensuring people are vaccinated as quickly as possible is the right thing to do. All adults getting a first dose by July is welcome, though if supplies increase this could be achieved earlier.
“We now urgently need Government to set out how they will prioritise those outside of the first nine groups – it’s perfectly reasonable for teachers, police officers and other key workers who haven’t been able to stay at home in the lockdown to ask when their turn will be.
“If Government aren’t going to prioritise by occupation in the next phase they need to set out why.
“Vaccination must go hand-in-hand with measures to break transmission chains. That means paying people decent financial support to isolate, updating face coverings guidance and insisting in ventilation standards to ensure all workplaces are Covid secure.”
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