Matthew Taylor chief executive of the NHS Confederation, acknowledged staff absence “is a huge issue for the NHS right now” but said the case for amending isolation rules further needs to be made clear.
At present, people who receive negative lateral flow results on day six and day seven of their self-isolation period – with tests taken 24 hours apart – no longer have to stay indoors for a full 10 days.
Calls are growing on the Government to cut this further after the US slashed its self-isolation period to five days if people are not showing symptoms.
The US Centres for Disease Control said most transmission of the virus happens in the two days before and three days after symptoms develop.
Speaking to BBC Radio 4’s Today programme, Mr Taylor suggested he had not seen a process where the evidence on cutting isolation could be assessed.
He said: “The Government, with scientific advice, has to make an assessment of the balance of risk here, but it’s important to recognise that there are risks to anything that we do, and if we were to reduce to five days that would have to be based on very clear evidence that is not going to increase the rate of infection.”
He pointed to Omicron being a new variant and the fact that Covid hospital admissions are still rising.
“The news about the acuity of those patients is good,” he said.
“It seems as though they are suffering less bad symptoms, and indeed many people who’ve got Covid are not coming to hospital because of Covid and it’s then been subsequently found out – that’s good.
“It’s also important to recognise the hospitals are full of people who are very vulnerable and, for those people, even a relatively mild form of the virus can have serious consequences, so whilst anyone in the NHS would be delighted if people were able to come back to work earlier, if they are safe, we need to be absolutely sure that that is the case.”
Shadow work and pensions secretary Jonathan Ashworth also said the Government should avoid “rushing into” cutting Covid isolation times.
Asked about reducing it to five days, he told Sky News: “I think we should always follow the advice of our leading scientists, medical scientists like Chris Whitty and Patrick Vallance, and I don’t think they’ve given an opinion on this.
“Let’s see what they say on this before rushing into this.”
On Tuesday, NHS Providers boss Chris Hopson said many in the health service now fear staff shortages caused by people isolating could represent a “bigger challenge” than the number of patients needing treatment for Covid.
And Professor Sir John Bell an immunologist from the University of Oxford, said lateral flow tests are “quite a good way of marking who is infectious and who isn’t”.
Pressed on whether he would back a five-day quarantine, he said: “If it was supported by lateral flow data, yes.”
The latest NHS data on hospital admissions suggests 71% of Covid patients in hospitals in England on December 21 were primarily being treated for the virus.
The remaining 29% were there “with Covid”, suggesting they tested positive on arrival for another ailment or tested positive during their stay.
Some medics are calling this latter group incidental Covid patients.
Dr Raghib Ali, a consultant in acute medicine at Oxford University Hospitals, said probably half the cases he is seeing are incidentals, though the pressure on hospitals overall remains high.
He has said that “when the prevalence of a virus with relatively mild symptoms is high in the community, then you will see higher incidentals”.
NHS data shows 8% of Covid patients in England on Tuesday were in beds requiring ventilators, compared with 13% at the start of the month.
Across the UK, some 842 people with Covid were in ventilator beds on December 22, compared to a peak of 4,076 on January 22.
Dr Chaand Nagpaul, chairman of the British Medical Association’s council, has suggested that Boris Johnson has ignored “the elephant in the room” of staff absence levels.
About 43% of NHS absences in London were currently because of Covid, compared to about 16% before the Omicron coronavirus variant first appeared at the end of November, he told the Financial Times.
Dr Ian Higginson, vice-president of the Royal College of Emergency Medicine, also said its recent survey suggests emergency departments were typically losing up to 25% of their nursing and medical staff because of either sickness or self-isolation from Covid.
Elsewhere, Leyla Hannbeck, chief executive of the Association of Independent Multiple Pharmacies, said the current daily supply of almost 900,000 lateral flow tests is not enough to meet demand.
She told the Today programme that people are turning up to pharmacies for lateral flow tests approximately every five minutes and often cannot get any due to low supplies.
“It just simply isn’t enough to meet the demand and it’s patchy,” she said.
“Some days you get one box delivered and other days none. It isn’t enough for the pharmacies to deliver to the patients.
“We want to make sure that the message is clear to the Government that the supply needs to be consistent.”
Meanwhile, Scotland’s First Minister Nicola Sturgeon is due to give an update on Covid restrictions as case numbers reach record highs.
England and Wales saw a record 129,471 confirmed cases on Tuesday, while separate figures for Scotland showed another 9,360 cases.
No data was available for Northern Ireland.
The Scottish Government introduced new measures on December 26, including one-metre physical distancing at large events, with limits of 100 people standing indoors, 200 people sitting indoors and 500 people outdoors.
New rules on social gatherings then came in on Monday, with meetings limited to three households at indoor and outdoor venues like bars, restaurants, theatres, cinemas and gyms.
Table service was also made a requirement at places where alcohol is served.
The Government in Westminster has said while the early evidence suggests Omicron is less likely to cause serious illness than earlier waves, it stands ready to impose new measures in England if necessary.
England is currently alone among the home nations in ruling out additional controls before the new year.