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 they are the "essential defence against Omicron".
Omicron - a coronavirus variant - could cause between 25,000 to 75,000 deaths by the end of April, according to new research.
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.