(Writes through with variants, results)
By Kate Holton and Alistair Smout
LONDON, Feb 20 (Reuters) - Britain has started to drive downcases of the more infectious South African variant ofcoronavirus and will only emerge from lockdown in stages to makesure that does not change, the country's health secretary saidon Sunday.
A day before Prime Minister Boris Johnson sets out his planto ease restrictions in England, Hancock said there was alsoearly data showing that the faster-than-expected vaccine rolloutwas reducing transmissions and easing pressure on hospitals.
Britain has the world's fifth-worst official COVID-19 deathtoll, with 120,365 fatalities, but an early drive to secure massvaccine supplies means one in three adults has now had a firstshot and daily death rates have started to fall.
Hancock said in total the United Kingdom had recorded around300 cases of the more infectious South African variant of thedisease that causes COVID-19.
"But most of those are now historic cases and from over amonth ago," he told the BBC's Andrew Marr show. "The latest datashows that there's around a dozen new ones, so a much, muchsmaller number."
England has also introduced hotel quarantines to preventvariants from travelling from abroad.
So far, Britain has given a first dose of a vaccine to 17.2million people, over a quarter of its 67 million population andbehind only Israel and the United Arab Emirates in vaccines perhead of population.
The government said on Sunday that all adults in Britainwould be offered a first shot by the end of July, with a targetto give a first dose to all over-50s by April 15.
But despite the improving picture, Hancock and leadingepidemiologist John Edmunds said the restrictions must be easedgently and in stages, to see what impact the increased movementof people has on the virus.
Hancock suggested each easing could require a couple ofweeks to detect the impact, before another part of the economycan reopen. Schools are expected to return first in early March.
Edmunds said it was difficult to say how widespread theSouth African variant was but that, like the rest of thepandemic, it was being held in place by the lockdown.
"The risk comes when we release the lockdown," he said,adding that allowing the virus to circulate in younger healthierpeople could lead to further mutations that undermine thevaccine programme.
Johnson will set out his thinking on the easing of lockdownon Monday. Despite pressure from a section of lawmakers in hisparty who have been shocked by the 10% contraction of theeconomy in 2020, the prime minister is expected to be wary.
"There should be no doubt - the route out of lockdown willbe cautious and phased, as we all continue to protect ourselvesand those around us," Johnson said in a statement.
(Editing by Ros Russell and Emelia Sithole-Matarise)