All adults in Britain will be offered a first shot of a COVID-19 vaccine by the end of July, Prime Minister Boris Johnson said on Saturday ahead of a planned announcement on the cautious reopening of the economy from lockdown.

Johnson will set out a roadmap to ease England’s third national lockdown on Monday, having met a target to vaccinate 15 million Britons from higher-risk categories by mid-February.

Britain now aims to give a first dose to all over-50s by April 15, the government said, having previously indicated it wished them to receive the shot by May.

If all adults receive a dose by the end of July, it will be well ahead of a previous target that they would receive a vaccine by autumn.

After suffering the world’s fifth-worst official COVID-19 death toll and a series of mishaps in its pandemic response, Johnson’s government moved faster than much of the West to secure vaccine supplies, giving it a head start.

Johnson cautioned that there was a need to avoid complacency, adding that lockdown would only be lifted slowly.

“We will now aim to offer a jab to every adult by the end of July, helping us the most vulnerable sooner, and take further steps to ease some of the restrictions in place,” Johnson said in a statement.

“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.”

So far, he United Kingdom has given a first dose of vaccine to 17.2 million people, over a quarter of its 67 million population and behind only Israel and the United Arab Emirates in vaccines per head of population.

Two vaccines – one made by Pfizer and BioNTech , and another developed by the University of Oxford and AstraZeneca – are being rolled out, and UK officials have advised that there can be a 12 week gap between doses.

British Health Secretary Matt Hancock said tougher border measures and enhanced contract tracing appeared to have restricted the spread of coronavirus variants from Brazil and South Africa.

Hancock said a roadmap to ease England’s third national lockdown, due to be published on Monday, would need to allow time to analyse the data because the government is still concerned the variants could undermine the vaccine roll-out.

However he told Sky News that the initial signs were encouraging.

“There is evidence that the measures that we’re taking, both the enhanced contact tracing and also the stricter measures at the border, there is evidence that these are working and that we’ve now got a much stronger vigilance in place.”

Prime Minister Boris Johnson will set out the roadmap on Monday, having got off to a faster than expected start with Britain’s vaccine roll-out programme.

“It is very important to see the impact of steps that we’re taking,” Hancock said of the next steps. “We want to set out a roadmap which gives people guidance in terms of how we think we’ll be able to do this. We also absolutely will be vigilant to the data on the way.

“We’ve currently seen other new variants that thankfully there’s very, very, very few of in this country now, but we’ve got to protect against them.”