All adults in England are being offered a Covid-19 booster.
The NHS national booking system has opened up to all over 18s as the health service ramps up its vaccination programme.
People are eligible for a booster three months after their second vaccine but they can book after two months.
It marks the NHS meeting its objective of offering every eligible adult a chance to book a booster before the New Year.
The health service is now racing to boost as many people as possible as it braces for the impact of a wave of Omicron cases.
Dr Emily Lawson, head of the NHS Covid-19 vaccination programme for the NHS in England, said: “The NHS Covid-19 vaccination programme, the biggest and most successful in health service history, is once again pulling out all the stops to protect the country from this cruel virus.
“Millions more people can book their booster from today and NHS staff are working flat out to set up more sites and put on extra appointments.
“This is by far the most complex but critical phase of the biggest and most successful vaccination drive and so with latest data showing that the booster is our best hope of protecting people against the new variant, it is vital people come forward as soon as possible by booking their slot online to guarantee that vital jab.”
Health and Social Care Secretary Sajid Javid said: “We are turbocharging the vaccine rollout to ensure as many people as possible can get boosted now as we continue our fight against the Omicron variant.
“From today, every adult in England who had their second dose two months ago can pre-book an appointment for that vital top-up jab.”
It comes after Professor Wei Shen Lim, chairman of the Covid-19 panel of the Joint Committee on Vaccination and Immunisation (JCVI), said that it was important to give the booster before the Omicron wave comes.
He told the Science and Technology Committee of MPs on Tuesday: “You want to give the booster before the wave comes, there is less benefit in giving a booster in the middle of a wave or after a wave.”
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