Scientists tracking the spread of coronavirus in England say infection levels in the community may have risen at the start of the latest lockdown.
Swab tests indicate 1.58% had the virus during the period 6-15 January, with the highest level, 2.8%, in London.
The Imperial College London researchers say there was “no strong evidence” of these high infection levels falling.
The past few days have seen a clear slowdown in the number of lab-confirmed cases reported daily by the government.
But the Imperial College London researchers say their data – based on swab tests from 143,000 people across England, of which nearly 2,000 were positive for the virus – is more up to date because it does not rely on those being tested developing symptoms and then waiting to have their infections confirmed by a laboratory.
The researchers say the government’s latest daily case figures may reflect a drop in cases just after Christmas, which is only now being registered.
And they suggest infection levels may have gone up in early January as a result of people’s activity increasing after the Christmas holiday period.
They admit there is some uncertainty in their data amid a “fast-changing situation” but conclude health services will remain under extreme pressure.
Ministers say the Imperial College London report does not yet reflect the impact of the national lockdown in England.
The UK recorded another all-time high of daily coronavirus deaths on Wednesday. A further 1,820 people died within 28 days of a positive Covid test, according to government figures – taking the total number of deaths by that measure to 93,290.
In an interview with broadcasters, Prime Minister Boris Johnson said there will be “tough weeks to come” but he hoped there would be a “real difference” by spring as the vaccine programme accelerates.
It comes as another 60 NHS Covid-19 vaccination centres in England, including a mosque in Birmingham and a cinema in Aylesbury, will welcome their first patients later.
Ministers have sought to reassure people in the top four priority groups for the Covid vaccination that they will get their jab by the government’s mid-February target, following complaints from some GPs about unpredictable supplies.
Some 4.6m people in the UK have now received the first dose of a Covid vaccine.
The director of the Imperial College London programme, Prof Paul Elliott, said the third lockdown was not having the same impact as the first, in April.
Facebook mobility data, which tracks people’s movements, suggested a fall in activity at the end of December but a rise at the start of the new year.
And Prof Elliott said everyone should “reduce their mobility as much as we can”.
A new, more transmissible variant and the fact larger households and deprived communities were more likely to be affected, may also be factors.
The latest round of results from Imperial College’s React-1 infection survey are interim and have not yet been published.
The survey is one source of data used to estimate the UK’s reproduction (R) number, along with other surveys, from the Office for National Statistics (ONS) for example, and figures on confirmed cases and hospital admissions.
The researchers hope to recruit people who have been vaccinated to future surveys but added it would be “a large number of weeks or months” before that was possible.
Prof Elliott said the data would be monitored closely.
“To prevent our already stretched health system from becoming overwhelmed, infections must be brought down,” he said.
“If prevalence continues at the high rate we are seeing, then hospitals will continue to be put under immense pressure and more and more lives will be lost.”
Health and Social Care Secretary Matt Hancock said the React findings showed “we must not let down our guard over the weeks to come”.
“It is absolutely paramount that everyone plays their part to bring down infections,” he said.
“This means staying at home and only going out where absolutely necessary, reducing contact with others and maintaining social distancing.”