Boris Johnson is awaiting new data on the effects of vaccines on coronavirus after stressing he will take a “cautious and prudent approach” to easing England’s national lockdown.

The Prime Minister is understood to be expecting updated evidence of jabs’ affect on hospital admissions and deaths to be with him by the end of Friday, ahead of setting out his “road map” next week.

But it was unclear whether the early data would include vaccines’ effect on transmission, with the results of two key Public Health England (PHE) studies possibly not available until next month.

Mr Johnson stressed on Wednesday that any easing of restrictions needs to be in stages and in an “irreversible” way as he was urged to focus on the evidence rather than deadlines when lifting restrictions.

During a visit to a mass vaccination centre in South Wales, he was asked about a call from the Ministry of Defence’s chief scientific adviser, Professor Dame Angela McLean, for any unlocking to be based on “data, not dates”.

“I do think that’s absolutely right,” the Prime Minister told reporters.

“That’s why we’ll be setting out what we can on Monday about the way ahead and it’ll be based firmly on a cautious and prudent approach to coming out of lockdown in such a way to be irreversible.”

Mr Johnson will consider evidence on how vaccines have been affecting coronavirus case numbers, hospital admissions and deaths before detailing his plans on Monday.

However, two key PHE studies on the impact of vaccines on the transmission of Covid-19 – the Vivaldi study on care home residents and staff, and the Siren research on healthcare workers – may not be available until next month.

Analysis by the PA news agency found coronavirus case rates for three of the four UK nations have dropped to their lowest level since early autumn 2020.

Both Wales and Northern Ireland are currently recording rates last seen at the end of September, while the overall rate for England has fallen to its lowest level since the start of October.

London and south-east England are also recording regional rates that are the lowest since October, according to calculations by PA from the latest health agency data.

Meanwhile, Dame Angela was asked if the R value, which measures the average number of people an infected individual passes the disease on to, needs to be at a certain level before restrictions can be eased as she appeared before the Commons Science and Technology Committee.

“I think the timing is probably more important; it’s how many of the people who are more at risk of, that’s a mixture of old people or people with underlying conditions, have been vaccinated before we do more unlocking,” she told MPs.

“The important issue is to really watch very closely what is happening, so if infections start to increase, and that we do everything we can to decide whether it is a good moment to take another step in unlocking.

“Let’s use data, not dates.”

She warned against unlocking too fast and said it risked “disaster” if some of the most vulnerable groups were still unvaccinated.

It came as:

– Government figures showed that 15,940,972 people have received coronavirus vaccines in the UK, a rise of 364,865 on the previous day.

– A further 738 people had died within 28 days of testing positive for Covid-19 as of Wednesday, bringing the official UK death toll to 118,933.

– Scotland’s First Minister Nicola Sturgeon said the latest report from National Records of Scotland (NRS) indicated vaccinations are reducing the death toll from coronavirus.

– Mr Johnson has said he is “reluctant” to link high coronavirus death rates in the South Wales valleys to austerity measures imposed by previous UK Governments.

– The world’s first coronavirus human challenge study will begin in the UK within a month, following approval from the UK’s clinical trials ethics body, the Department for Business, Energy and Industrial Strategy announced.