It's 'impossible to say' whether better, quicker testing would have avoided some of the UK's grim toll of care home deaths, a medical chief has said.
Yvonne Doyle said experts are trying to learn the answer after 3,811 deaths outside hospital since March were included in daily figures for the first time.
The Medical Director of Public Health England told the Mirror that in some ways, testing would not help - as some elderly residents died so quickly, they were not able to get a test.
But she also said the "movement of staff" - who were not routinely tested in care homes until a fortnight ago - was "critical" in how Covid-19 is spread.
She added: "I think there are possibly more fundamental and structural issues about how care homes are run in an epidemic that we are now looking to implement."
Tests for Covid-19 in care homes were severely limited until April 15, when the government widened capacity.
On that date, Health Secretary Matt Hancock announced officials would start testing people who had been discharged into care homes from hospital.
This suggested those patients had, in some cases, not been tested before then.
And he ended the policy of testing only five people with symptoms in a care home to confirm an outbreak, rather than everyone to know exactly who had the virus.
Care home staff with symptoms were only able to get tested routinely from April 15.
Before that date there had already been between 1,000 and 3,000 deaths recorded in care homes, official figures show.
First Secretary of State Dominic Raab also accepted the "ebb and flow" of staff into a care home, as well as friends and family members, was a crucial factor.
He was asked the same question by the Mirror at the government's daily press conference.
He said: "There's always learning in an unprecedented, unique crisis that we'll want to feed back in so that we can refine and fine tune the measures we're taking.
"We take the actions and the steps that we take based on the best scientific evidence that we've got at the time."
Prof Doyle said: "What we have learned a lot about is how the virus in different populations.
"And one of the very sad things that we have found is that when older people get this virus - it is affecting predominantly older people, people over 75 - one of the reasons the deaths are high there is that actually the demise quite quickly if they get the dose of this virus that perhaps a younger person might be able to put over the shoulder because of the way their immune system works.
"So it may not even have been possible to have got to the test by the time the event happens.
"Second we've also learned by looking at the literature that we've asked what is it that will stop the spread of this virus in a home.
"And the movement of staff is an absolutely critical one and how the virus actually moves within a home.
"Whether testing would have made a difference or not is impossible to say at the moment and that's what we want to learn.
"There has been testing, but I think there are possibly more fundamental and structural issues about how care homes are run in an epidemic that we are now looking to implement."
