The rollout will carry on during Christmas Eve, Christmas Day and Boxing Day, with around 200,000 appointments for a third dose still available across the country over the festive period.
Jenny Harries, head of the UK Health Security Agency, said the impact on society of Omicron will be crucial despite mounting evidence that it is generally milder than the Delta strain.
Jeremy Farrar, a former SAGE member, pointed out that while another booster is already being mooted in the UK, many around the globe have yet to receive a first jab.