More than 3.8m people have received a first dose of vaccine UK-wide - around a quarter of the 15m the government hopes to vaccinate by 15 February.
More than half of patients aged over 80 have now received a first dose of vaccine, the government has said - with more than quarter of a million doses a day now being administered.
The vaccination campaign has been focused to date on the top two priority groups identified by the Joint Committee on Vaccination and Immunisation (JCVI) - covering care home residents and staff, over-80s and health and care workers.
From 18 January the campaign will expand to the third and fourth priority groups, covering patients over 70 years old and those who are clinically extremely vulnerable. The top four cohorts in total account for 15m people in the UK, and around 12m in England.
However, the rollout will not extend to all over-70s and patients who are clinically extremely vulnerable at this stage, because the government has made clear that the first two groups 'remain the priority'.
A government statement makes clear that only 'vaccination sites that have enough supply and capacity for vaccinating further people are allowed to offer vaccinations to the next two cohorts'.
The move is intended to allow areas that have already provided a first dose of vaccine to most care home patients, health and care staff and over-80s to 'keep up the momentum and start vaccinating further at-risk people'.
Plans to widen the rollout of COVID-19 vaccination come after evidence that areas worst-hit by the pandemic in England were lagging behind on administering the vaccine.
Responding to the plan to begin vaccinating the next two cohorts of patients, prime minister Boris Johnson said: 'Today is a significant milestone in our vaccination programme as we open it up to millions more people who are most at risk from COVID-19.
'We are now delivering the vaccine at a rate of 140 jabs a minute and I want to thank everyone involved in this national effort. We have a long way to go and there will doubtless be challenges ahead - but by working together we are making huge progress in our fight against this virus.'
Health and social care secretary Matt Hancock said: 'Now that more than half of all over-80s have had their jab, we can begin vaccinating the next most vulnerable groups. Where an area has already reached the vast majority of groups 1-2, they can now start opening up the programme to groups 3-4.
'We are working day and night to make sure everyone who is 70 and over, our health and social care workers and the clinically extremely vulnerable are offered the vaccine by the middle of February and our NHS heroes are making huge strides in making this happen.
'This measure does not mean our focus on getting care homes, healthcare staff and those aged 80 and over vaccinated is wavering - it will remain our utmost priority over the coming weeks to reach the rest of these groups.'