Nonetheless, he is still facing pressure from lockdown sceptics on his Conservative backbenches to completely lift it as soon as possible.
The COVID Recovery Group has long been calling for all restrictions to be removed when people in the priority groups – over-50s, care home residents, clinically extremely vulnerable people, over-16s with underlying health conditions and frontline health and social care workers – have received a vaccine. The government’s target date for this is the end of April.
Speaking on the BBC’s Question Time on Thursday, chair Mark Harper said: “Our view is once you’ve vaccinated those people and reduced hospitalisations by 80%, then you can remove the domestic restrictions."
In contrast, Scientific Advisory Group for Emergencies (Sage) adviser Prof Stephen Reicher said it would be an “appalling idea” to “open everything up and let the infection rip” even after the vulnerable groups have been vaccinated.
Watch: Boris Johnson says lockdown lift will be 'cautious' (from Wednesday)
Speaking at an Independent Sage briefing on Friday, he set out three reasons why:
1. Younger people still get infected...
...and still have to go to hospital.
As of Friday, 128,566 people in the 18 to 64 age group had been admitted to hospital with COVID in England (see below) since the start of the pandemic – most of which has been spent under some form of restrictions.
2. 'Long COVID'
Prof Reicher said opening up too soon could also “condemn” some people to the long-term effects of having the virus, also known as “long COVID”.
Research released on Friday showed one in four patients have trouble coping at home after discharge from hospital.
3. 'Free pass' for new vaccine-resistant variants
Prof Reicher also warned “letting the virus rip” could eventually damage the effectiveness of vaccines.
"If you let the infection rip, let it circulate, in effect you give it a free pass to find new ways around the vaccines. The more infections, the more mutations, the higher the probability of new variants getting past the vaccines."
He concluded: "Those who say open up immediately… are actually suggesting something incredibly damaging, ignoring the realities."
Independent Sage, meanwhile, has said shops and pubs should only reopen in an area when it has less than 10 cases per 100,000 people.
It also said schools should only reopen when infections are less than 100 per 100,000 people across all regions.
So far, the only thing Boris Johnson has confirmed is an 8 March target date “at the earliest” for schools to reopen.
Watch: What is long COVID?