The move to favour alternatives to the Oxford/AstraZeneca vaccine for under 30s will not delay the easing of the lockdown or affect the deadline to offer jabs to all adults, ministers have said.

Prime Minister Boris Johnson said on Wednesday that he sees no reason to “deviate from the road map” to relax England’s restrictions “in any way”.

Health Secretary Matt Hancock said the nation remained “on track” to offer a first dose to all adults by the end of July, a message echoed by deputy chief medical officer Professor Jonathan Van-Tam.

Their assurances came as the official advice from the Joint Committee on Vaccination and Immunisation said under 30s should be offered alternative jabs to AstraZeneca.

The UK’s advisory body made the precautionary change because of evidence the vaccine may be linked to very rare blood clots.

The move means the Moderna and Pfizer jabs will now be favoured for the 18-29s who do not have underlying health conditions putting them at higher risk of severe Covid-19.

Mr Johnson said the Government would accept the advice and vowed there would be no delay to the lockdown-easing plans.

“I don’t see any reason at this stage at all to think we need to deviate from the road map and we’re also very secure about our supply,” he told broadcasters during a visit to Cornwall.

Professor Van-Tam said the change in advice for the Oxford/AstraZeneca vaccine should not slow the wider rollout of jabs.

“The programme should not be delayed because of this change in course, everything should stay on course,” he told a televised briefing.

But the medical adviser acknowledged there may be “a small delay sometimes” for individuals and there “might be a slightly greater distance” that some may have to travel.

“But the NHS is all over this and understands the challenge of making the advice from JCVI truly operational in a smooth way,” he added.

More than 60% of UK adults are estimated to have received a first dose, with Government data up to Tuesday showing 31,707,594 people had received at least one vaccine.

The latest development for the vaccine programme came a day after it emerged that official estimates for supplies were sharply downgraded.

The Cabinet Office indicated an average of 2.7 million doses a week will be given in England until the end of July, down from a previous estimate of 3.2 million.

Supplies of vaccines in April were constrained by the need to test a batch of 1.7 million doses as well as delays in a shipment of around five million from India.

But the department’s scenario, provided to experts on the Scientific Pandemic Influenza Group on Modelling (Spi-M), suggested the supply issues may continue for months.

Papers produced by Spi-M on February 17 were based on an average of 3.2 million doses a week until the end of July and 3.9 million thereafter.

Spi-M said the central scenario provided by the Cabinet Office for its March 31 paper was “considerably slower”, with 2.7 million weekly doses until the end of July and two million from then on.

A slower scenario suggested that just 2.5 million weekly doses might be available.

The Spi-M summary notes that the two scenarios produced by the Cabinet Office “may not reflect the situation most likely to occur”.