People aged 23 and 24 will be invited to book their first dose of the vaccine from June 15.
This next wave of vaccination is part of the government's drive to offer every adult in England a first dose of the vaccine by July 19.
The new target - advanced from an initial date of July 31 - will also see the country enter the next stage of reopening, after a four week delay was announced on June 14.
Over 75 per cent of UK adults have now received their first dose of a Covid-19 vaccine and over half of adults are fully vaccinated.
In the last week the Government has delivered around 170,000 first Covid vaccine doses a day. At that rate, some 4.5 million more first doses could be delivered in the four-week delay to reopening that is expected to be announced today.
Downing Street’s argument for the extension is that it buys the country more time to both monitor the Delta variant – first found in India – and, crucially, deliver millions more doses of the vaccine.
And if they shorten the time that people in their 40s have to wait for their second jab – as Scotland did this weekend – analysis suggests they could deliver as many as 12 million jabs.
A total of 41,551,201 people have received a first dose as of June 13, while 29,792,658 second doses have been given out since the rollout began on Dec 8, with those aged 25 and over being invited forward to receive a dose in England.
Although there is no set date for those under 25 to receive a vaccine, many over-18s have been able to get a jab as local pharmacies, GP surgeries and clinics aim to use up spare doses or are increasing capacity.
Three vaccines are now in use - Pfizer, AstraZeneca and Moderna - and the single-dose Johnson & Johnson vaccine (Janssen) was approved for use in the UK as of May 28.
The Government has ordered 20 million doses, which will be used to target "hard-to-reach" groups in the vaccine rollout, such as those who may be reluctant to come forward for two jabs. Additionally, the Janssen vaccine will potentially be used as part of a booster programme later in the year.
The Medicines and Healthcare products Regulatory Agency (MHRA) approved the use of the Pfizer vaccine in 12- to 15-year-olds on June 4.
Who is currently eligible for a vaccine?
People aged 25-29 are now being offered the coronavirus vaccine, with 23 and 24 year-olds to be invited from June 15.
The NHS website for booking Covid vaccinations crashed on June 8 as hundreds of thousands of young people queued to book nearly half a million slots. Health service bosses saw an average of 100,000 vaccine appointments scheduled every hour on the first day of the jab being made available to this age group.
In Wales, booking is already open to all people over the age of 18, while in Northern Ireland for those aged 25 and over.
Under advice from the Joint Committee on Vaccination and Immunisation (JCVI), people under 40 are offered Pfizer or Moderna, rather than AstraZeneca due to the link with rare blood clots.
The same recommendation has been made for pregnant women, who can access the national booking service to ensure they are sent to sites with Pfizer and Moderna.
In response to the rise in the numbers of cases of the Indian variant, the Government wants to vaccinate as many as one million people a day as part of a drive to save the British summer.
In promising news, vaccines against new coronavirus variants should be ready by October, the team behind the Oxford University/AstraZeneca jab said, after The Telegraph revealed that Britain would have the capacity to vaccinate the entire nation against new coronavirus strains within four months, once a new “super-factory” opens this year.
In an interview with The Telegraph, Nadhim Zahawi, the business minister, revealed over-70s will start to get booster Covid vaccines from September to protect them from new virus variants. The plan will see some people have three doses within the first 10 months of the jabs being in use.
The first booster doses will go to people in the top four priority groups for the original rollout – those aged over 70 as well as frontline NHS and social care workers.
Military labs are to quadruple testing in the battle against Covid variants, it was confirmed on May 5. Ministers have pledged a £30m investment to facilitate weekly testing at the military laboratory Porton Down. This is part of government planning to safeguard the progress of the roadmap out of lockdown and the future of public health moving forward.
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How will I be invited to get the vaccine?
The NHS will contact you when you are eligible for the vaccine and you will be invited to make an appointment.
If you are registered to a GP, you will be contacted by your surgery either over the phone, by text, email or post, in order to book in to receive a vaccine at your local vaccination centre.
You can still register at a GP surgery if you are not already registered to one, and it is advised that you make sure that your contact details are up to date to ensure that there are no delays.
However, if you are over 50 and have still not taken up an offer of the vaccine, the Government urges you to contact your GP.
Alternatively, you can check whether you are eligible and find an appointment by using the NHS vaccination booking service or by calling 119.
Why is there a delay between the first and second jabs?
Regulators have said the key to success will be to administer two full doses between four to 12 weeks apart, in order to give as many people as possible the initial dose of the vaccine, which offers some protection from the virus.
However, the rollout of second doses has been accelerated following concerns about the spread of the Indian variant.
A study found a single dose of the Oxford vaccine was 76 per cent effective in fending off infection between 22 days and 90 days post-injection, rising to 82.4 per cent after a second dose, while a different study found that a single dose of the Pfizer vaccine provided a "very high" level of protection (90 per cent) from Covid-19 after just 21 days, without the need for a second "top-up" vaccination. The UEA study, which has not yet been peer reviewed, looked at data from Israel.
Those who had received the Pfizer jab were 49 per cent less likely to transmit the virus to others in their households, while transmission fell by 38 per cent for those given the AstraZeneca vaccine.
According to data released on May 20 by PHE, a fortnight after the first dose of the Pfizer or AstraZeneca vaccine, the chance of getting symptomatic Covid fell by nearly 60 per cent, with a second dose bringing this up to 90 per cent.
The PHE data examined cases of coronavirus among those aged 65 and over, who were in the first groups to get vaccinated.
While it is not yet known how long immunity lasts beyond 21 days without a second dose, researchers believe it is "unlikely" to majorly decline during the following nine weeks.
What about the new variants of coronavirus? Will the vaccine still protect us?
The emergence of new Covid-19 strains, such as the South African, Indian (or Delta) and Brazilian variants, have threatened to undermine the vaccine and testing gains of recent months.
PHE estimates that the Delta strain is 60 per cent more transmissible than the Kent or Alpha variant, with cases doubling every four and a half days in some parts of England.
Hopes for a full reopening in the near future have also been affected partly by the news that both the Pfizer and AstraZeneca jabs give only 33 per cent protection after one dose, compared with up to 80 per cent protection against previous variants.
This comes as the Prime Minister announces that the planned reopening on June 21 has now been delayed four weeks to July 19.