A record one million Covid-19 vaccines were booked in a single day when over-25s in England became eligible for the jab.
The NHS said that a record-breaking number of vaccine appointments were booked on Tuesday as those aged 25 to 29 in England were able to book an appointment for the first time.
There was a “Glastonbury-style” surge of traffic on the NHS website, officials said.
At the height of action on the “blockbuster” day, 100,000 appointments were being booked every hour.
A number of young people initially reported problems booking, either with long queues or being told they were ineligible to book.
The issues were quickly resolved and NHS England said the National Booking Service had 493,000 appointments reserved by midday on Tuesday, just five hours after over-25s were included.
A total of 1,082,596 first and second dose slots were booked throughout the day – four times the number booked on Monday.
The record bookings will be welcome news as the country continues the so-called race of vaccines against variants.
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The Delta variant (formerly known as the Indian variant) has now become the dominant in the UK and is thought to be 40% more transmissible than the Alpha (otherwise known as Kent) variant.
While two doses of both vaccines are almost as effective against the Delta variant as they are against the Alpha variant, one dose of either only offers around 33% protection.
The increasing cases and dominance of the Delta variant means that the date of June 21 for all coronavirus restrictions in England to end is looking less and less likely.
Officials have said previously that opening up appointments to under 30 marked the “home straight” of the vaccination campaign which only launched six months ago.
The head of the NHS in England said the figures have dispelled the suggestion younger people may shy away from vaccination.
Sir Simon Stevens said: “Enthusiasm for the biggest and most successful vaccination programme remains strong as bookings for the lifesaving jab reached an all-time high yesterday and the obvious enthusiasm of younger adults to get their jab has blown out of the water the suggestion that people in their 20s might not come forward to protect themselves and their loved ones.
“The Covid-19 vaccine is still the best protection against coronavirus and as further supplies become available to us week by week it’s great that we’ve seen 25 to 29-year-olds sending bookings to blockbuster levels, following hard on the heels of the millions of others.
“Getting the lifesaving Covid-19 jab is the most important thing you can do, so book your appointment and get that vital protection.
“Remember: when you get the text, you’re next.”
Grandmother Margaret Keenan, 91, became the first patient in the world to receive a Covid-19 jab outside a clinical trial when she was given the Pfizer/BioNTech vaccine in Coventry on December 8.