Latest test and trace figures for England show the number of people testing positive for coronavirus fell by 19% in the week to 24 February.
New study finds virus decline slowing in England.
A marked decline in infections between January and February may have slowed, according to scientists tracking coronavirus in England.
Infections have fallen by two-thirds over lockdown but one person in 200 still has the virus.
Lower virus levels are needed to get the best out of the vaccination programme, Imperial College's React study says.
Based on swab tests of a random sample of 165,000 people between 4 and 23 February, the study estimates 0.5% of people in England had the virus - down from 1.57% in January.
The figures show "substantial falls" in household infections in all age groups and in most regions since early January, while lockdown restrictions have been in place.
It comes as official figures continue to show sharp falls in confirmed cases, hospital admissions and deaths linked to Covid-19 going back several weeks.
But the React study finds some evidence of smaller falls in Yorkshire and the north-east, and apparent rises in London, the south-east and the Midlands - although this is based on only a few days' worth of data in February.
But a "promising" six-week decline in Covid cases in Europe has been disrupted by a rise in infections, the World Health Organization says.
"We are seeing a resurgence in central and eastern Europe," says Hans Kluge, the WHO regional director for Europe.
New cases are also rising in several western European countries, Kluge adds, saying Europe needs to expand supply and access to vaccines.
Germany is changing its stance on the Oxford-AstraZeneca vaccine, allowing over-65s to receive the jab, Chancellor Angela Merkel says.
UK Chancellor Rishi Sunak says the "shock that coronavirus has done to our economy has been significant" and "won't be fixed overnight".
It "will be the work of many years, decades and governments to fully pay all that money back," Sunak says
New vaccines to fight variants such as the one from Brazil can be fast-tracked through the approval system, says UK regulator the MHRA.
US President Joe Biden has criticised the lifting of mask requirements in the states of Texas and Mississippi, calling it "Neanderthal thinking".