People aged 30 and over in England will be able to book a Covid-19 booster jab from Monday.
Health and Social Care Secretary Sajid Javid said data shows boosters are the “essential defence against Omicron”.
Booster vaccinations are now being given three months on from a second dose – rather than after six months.
Omicron – a coronavirus variant – could cause between 25,000 to 75,000 deaths by the end of April, according to new research.
Education Secretary Nadhim Zahawi told the Andrew Marr programme on Sunday that “we are still learning about this variant, [but] we know boosters work, get [a] booster.”
Some people under 40 reported being able to book their booster jab appointment online over the weekend, as the programme extends.
Scientists from the London School of Hygiene and Tropical Medicine (LSHTM) say the UK will face a substantial wave of Omicron infections without further restrictions beyond Plan B.
These numbers are only a projection, rather than a prediction, and scientists say there is still uncertainty around the modelling.
The UK announced a further 54,073 new cases on Saturday, including 633 of Omicron – although the real number of Omicron cases is estimated to be much higher.
Dr Nick Davies from LSHTM said Omicron was likely to be the dominant form of the virus in England by the end of the year.
Prof Sian Griffiths, professor of public health at the University of Hong Kong and visiting professor at Imperial College London, said booster jabs could become a regular occurrence, depending on how coronavirus continued to evolve.
“It may well be that we need to keep this as a rolling programmed,” she said.
This week, so-called Plan B measures have been introduced in England including mandatory face coverings in most indoor public venues and on public transport.
People have been asked to work from home where possible from Monday, and care home residents will be allowed only three visitors and an essential care giver.
NHS Covid Passes – which show you are fully vaccinated, have had a recent negative lateral flow or PCR test, or have an exemption – will be needed to enter some large-capacity venues in England from 15 December.
On Tuesday, parliament will take three votes on the new measures – with a rebellion from about 60 Tory MPs expected on the introduction of Covid passes.
There is also expected to be a vote on mandatory vaccination for frontline NHS staff in England.
Labour leader Sir Keir Starmer said his party would “not be tempted to play party politics” and would back the government in voting for the measures “in the public interest”.
Conservative MP Steve Baker, a lockdown sceptic, told BBC Breakfast he would vote against mandatory vaccinations, Covid passes and extending face covering rules.
He said scientific modelling was “pessimistic”, such measures were “disproportionate” and said people needed to learn to live with coronavirus “like we live with flu”.
In Scotland, household contacts of people who have tested positive for Covid are now being asked to isolate for 10 days – regardless of their vaccination status or if they have had a negative PCR result.
The Scottish government has also said adult care home staff and those working in social care who get vaccinated during work time will not lose out financially or have to take annual leave to do so.
The Welsh government is urging members of the public to take a lateral flow test before going shopping or to Christmas parties. It has also said rules will be reviewed weekly rather than every three weeks.
Officials in Northern Ireland are not planning to extend restrictions over the festive period but further curbs may be reintroduced in the new year.
More than 22 million people in the UK have now had a third vaccination or booster.
The Joint Committee on Vaccination and Immunisation (JCVI) recommended in November the window between second jabs and boosters be reduced from six months. It also said all over-18s would be offered the booster.
Dr Emily Lawson, head of the NHS Covid vaccine programme, said the NHS was continuing to look for volunteers to help with vaccine delivery.
“Please do look at the opportunities available. You would be helping us to save lives,” she said.