Science Editor Tom Clarke reports that in England, an increase in cases is driven to a great extent by those who are younger and not yet vaccinated.
All adults in England will be able to book their Covid-19 vaccine from Friday, as eligibility is extended to everybody over 18.
The Health Secretary announced at the NHS Confed Conference that over-18s will soon be able to book using the National Bookings Service.
Matt Hancock said four in every five adults in England now has their first jab.
It comes as ministers consider proposals to allow people who have had both jabs to head on quarantine-free holidays abroad this summer.
The proposal would allow people who have had both jabs to avoid quarantine on their return from amber list countries - making them essentially green - but testing will still be required.
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Mr Hancock told the conference on Thursday: "As of this afternoon we have given a first dose of vaccine to four out of every five adults in the United Kingdom.
"And the speed of deployment means that tomorrow we can open vaccination to everyone over the age of 18.
"I think it’s an incredible achievement on the vaccination side."
The government is racing to vaccinate every adult in the country before July 19, when the next stage of England's lockdown easing has been delayed until.
Public Health England confirmed on Thursday that case rates in the country are continuing to rise among all age groups.
The highest rate is among 20 to 29-year-olds, with 195.9 cases per 100,000 people in the seven days to June 13, up week-on-week from 123.6.
This is also the age group to see the biggest week-on-week increase.
The study, commissioned by the government, found that rising cases are also being driven by young people.
Between May 3 and June 7 infections doubled, which coincides with the rise of the Delta coronavirus variant which was first detected in India and is now dominant in the UK.