More than half the UK’s adult population has now received a first COVID vaccine dose, the health secretary has said.

“I’m delighted to be able to say that we’ve now vaccinated HALF of all adults in the UK,” Matt Hancock tweeted.

“The vaccine is a national success story and our way out of this pandemic.”

The midway point of the UK’s stated aim to vaccinate the whole adult population against COVID-19 by the end of July was passed in the last 24 hours.

It means Britain and Northern Ireland are just over five million short of their second target – vaccinating the first nine priority groups by the 15 April. Current progress means that the target will be achieved ahead of time.

Prime Minister Boris Johnson has set a target of offering a first dose of a COVID-19 vaccine to everyone aged 18 or over in the UK by the end of July 2021.

He made the pledge after the NHS met its first target of vaccinating everyone in the first four priority groups, some 15 million people, by mid February.

More from Covid-19

The speed with which that was achieved spurred the government to go further and set additional targets.

There are an estimated 52.7 million people aged 18 and over in the UK, according to the Office for National Statistics.

Vaccine take-up among older age groups has been high, with nearly 95% of those aged 80 and over having had the jab.

However. experts say it may become harder to reach younger age groups as time goes on as vaccine hesitancy is reportedly at much higher levels among those in their 20s and 30s.

There are also reports uptake of the vaccine has been slower among some Black, Asian and Minority Ethnic (BAME) communities.

What may slow down progress further is the need to provide second doses for everyone who has had a first dose.

Figures indicate that reports predicting an uptick in the speed of the vaccination process this week have been proved correct, with the UK breaking its record for the most coronavirus jabs given out in one day.

A total of 660,276 doses were administered nationwide on Thursday, latest government figures show. That includes 528,260 first jabs and 132,016 second doses.

But Mr Hancock has said it is unlikely that rate of progress will be matched in the coming month, after a need to retest more than one-and-a-half million vaccine doses – as well as delays to doses arriving from India – will lead to a “tighter” supply of COVID jabs next month.

It is too early to tell whether an EU threat to block jab exports to UK and other countries with high vaccination rates will make a further difference going forward.

The UK is someway ahead of the next nearest European country in the list of the countries to vaccinate the highest proportion of their populations, Malta, and the UK has vaccinated more people than any country other than the US.

Analysis: Huge milestone in our journey back to normal life

By Thomas Moore, science correspondent

Vaccinating half of all adults is another hugely significant milestone in our journey back to normal life.

The overwhelming majority of the most vulnerable people now have good protection from the worst effects of COVID.

That shows in the daily stats.

The fall in hospital admissions and deaths in the current lockdown has been far steeper than in the one last spring.

And that has a lot to do with the vaccine rollout, targeted first at those most at risk.

Real world data has shown that four weeks after the first dose the AstraZeneca and Pfizer jabs are respectively 94% and 85% effective at preventing hospitalisation.

The second dose, which many people are now receiving, will increase protection still further.

The month-long pause in rolling out the vaccine to younger adults increases the risks as lockdown is eased. Risks for individuals – men in their 40s have a one in 1,000 chance of dying if they become infected.

But risk, too, that the virus will spread more rapidly because more people than anticipated are unprotected by vaccination. That could affect the pace at which lockdown can be lifted.

But this is just a temporary supply glitch.

More doses will be available in May, including some of the new Moderna vaccine.

With the incredible will and energy of the health workers and volunteers in the vaccination centres the rollout will rapidly accelerate once again. In their sights now is the next big milestone – vaccinating all adults by the end of July.