We are - as ministers have repeatedly said - in a race between the vaccine and the variants. And Britain made a significant head start.
It is now more than six months since Margaret Keenan, 90, in Coventry, became the first person to receive a Covid vaccine outside of a trial.
On Monday, official statistics are set to show that more than 30 million people - approaching six in 10 adults - have had both jabs, while close to 42 million have had their first.
The Government’s target to offer first doses to the whole adult population by July 31 looks set to be comfortably met, with the rollout now working through those in their 20s.
Yet the Prime Minister will deliver the news that a more fundamental goal of freedom appears more elusive than ever. It is clear that next Monday - June 21 - will not be “freedom day”.
Ministers, scientists and medics have lined up in recent days to say that more needs to be known about the impact of the Delta variant, first seen in India, on hospitalisations, and on the effectiveness of vaccines, before significant lessening of restrictions could be allowed.
Delays could allow far more vaccines to be administered, they have suggested, with the Prime Minister this weekend saying: "It may be that in the race between the vaccines and the virus, we need to make sure we give the vaccines extra legs."
If the current pace of rollout continues, a delay of four weeks could allow an extra 12 million doses to be given; around four million more first doses, and eight million second jabs.
While latest data suggests that the vaccines are extremely protective - just five per cent of those hospitalised have had both doses - there is concern that the variant may cause more severe illness.
Modelling for the Scientific Advisory Group on Emergencies (Sage) suggests the variant could cause as a third wave with as many hospitalisations as the second, while estimates suggest is 60 cent more transmissible than the Kent variant.
Amid evidence that one jab offers inadequate protection against infection from the now-dominant variant, the pressure is on to get second doses out as quickly as possible, especially to those at greatest risk of hospitalisation.
Ministers say they are “on track” to get second doses to all over-50s a week today, having shortened the gap between first and second doses from 12 weeks to eight.
On Sunday, Dominic Raab, the Foreign Secretary, told the Andrew Marr programme: “The race we are in is to get everyone, as far as we possibly can, to two doses.”
But the Government appears reluctant to explain what that means.
The Scottish government announced on Sunday that it was bringing forward second doses for over-40s, reducing the interval between doses to eight weeks, as has been done for older groups.
The Westminster government has yet to announce such a plan.
If similar changes were made, around five million fortysomethings who are due a second dose in England could be offered one by July 5, and be fully protected by July 19.
But without an acceleration, the rollout of second doses risks stalling once the target for over-50s is hit, with the rollout only due to start reaching those in their late 40s two weeks later.
This weekend, the Prime Minister told ITV News: "We're looking at all the data but what we're wanting to do is avoid another wave of deaths that could be prevented by allowing the vaccines to work in the way that they are.
"It may be that in the race between the vaccines and the virus, we need to make sure we give the vaccines extra legs."
Speaking from the G7 in Cornwall, the Prime Minister was reluctant to answer an increasingly vexed question: what percentage of the population needs to be “double-vaccinated” before Britain proceeds to stage four in easing of lockdown?
The latest figures show 78 per cent of adults have received at least one jab, while 57 per cent have had two. But when considering herd immunity, the whole of the population must be considered.
When children are factored into the calculations - and ministers are awaiting advice from the Joint Committee on Vaccination and Immunisation about whether to to extend the programme to children - just 44 per cent of the UK has had both jabs.
On this - and on almost everything else about lockdown - Boris Johnson would not be drawn, only promising a “whole package of information” on Monday.