A third of people who catch Covid may still be infectious after five days, according to a study that illustrates the gamble ministers face in cutting the self-isolation time.
University of Exeter experts warned it meant a ‘potential risk of onward transmission’, given that tens of thousands of Brits are currently testing positive every day.
No10 yesterday confirmed it would slash the self-isolation period from seven days to just five in a bid to ease pressure on staff absences due to the Omicron variant.
Despite the news being welcomed by business leaders and MPs, medics today urged ministers to make health and care staff exempt. They warned patient safety would be at risk if potentially Covid positive NHS staff returned to work.
Separate data from the UK Health Security Agency, backing the University of Exeter study, estimated 31 per cent of people with Covid were still infectious five days after the onset of symptoms.
However, the number of infectious people released into society is reduced to as little as 5 per cent if people have two consecutive negative lateral flows, the Government agency said.
Health Secretary Sajid Javid confirmed the length of quarantine for positive cases is being reduced from the current seven days to just five
Responding to the five day self-isolation announcement, one of the authors of the Exeter study said their findings indicated nearly one in three people could still be infectious after five days.
However, independent experts have said the study is limited because it used samples of the original Covid variant and the findings have limited application to the current Omicron wave.
Experts admit there is a trade off in self-isolation periods – with a need to balance the disruption caused by so many people taking time off work to the economy, and the need to reduce the risk of infected individuals spreading the virus to others.
Professor Lorna Harries, a molecular genetics expert and one of the authors of the Exeter study, said: ‘Our data arise from research published today which uses a newly adapted test which can detect whether the virus is potentially still active.
‘Our data shows that at five days, 30 per cent of people still exhibited clinically-relevant levels of potentially active virus, meaning they may still be infectious.’
Professor Harries called on the Government to ensure supplies of lateral flow test kits keep up with demand and said specalised tests such as the one used in their study should be used in vulnerable settings such as care homes.
Health secretary Sajid Javid announced the change to self-isolation rules in England in the House of Commons yesterday.
Mr Javid told MPs that UKHSA data showed ‘that around two-thirds of positive cases are no longer infectious by the end of day five’.
He added that, from Monday, people will be able to take two tests to get out of isolation, ‘leaving isolation at the start of day six’.
‘I urge everyone to take advantage of the capacity we have built up on tests,’ he told the Commons.
Other UK nations have yet to announce if they will adopt a similar change or stick to a seven day Covid self-isolation period.
But some healthcare staff unions have revolted over the changes to self-isolation rules and have called for an exemption.
The Royal College of Nursing slammed the decision, with the trade union’s general secretary saying the changes put patient safety at risk.
‘By the Government’s own estimate, almost a third of individuals are infectious five days after symptoms starting,’ she said.
‘This change could increase the risk of transmission to other staff and patients.
‘When providing close care, including to those with compromised immune systems, nursing staff must be confident that they are not putting patients at risk.’
In the Exeter study, published in the Journal of Infectious Diseases, scientists took samples from 176 people who had tested positive for Covid on a PCR test.
Then using a modified version of the PCR test the scientists aimed to discover how long these people could potentially spread Covid.
Conventional PCR tests work by testing for the presence of Covid viral fragments but not if it the virus is still active, and therefore potentially infectious.
Using the modified test, the researchers found that 30 per cent of people still had ‘clinically-relevant’ levels of the virus, meaning they could be potentially infectious.
This decreased to 13 per cent after 10 days, though the study found some people maintained high levels of the virus for up to 68 days.
Professor Harries said: ‘There was nothing clinically remarkable about these people, which means we wouldn’t be able to predict who they are.’
But independent experts have said the findings of the study are limited, noting that the samples in the study were from 2020 before the rise of Covid variants such as Delta and Omicron.
Professor Paul Hunter, an epidemiologist at the University of East Anglia, added that just because someone has active Covid virus it doesn’t necessarily mean they are infectious.
‘We know from early studies that virus can be shed from as early as four days before to several weeks after symptom onset,’ he said.
‘But that doesn’t necessarily equate to infectiousness. Very few studies have attempted to measure when cases infect others.’
Professor Lawrence Young, a virologist at the University of Warwick, said: ‘The current study was based on infections analysed in samples taken in 2020 when the original Wuhan variant was dominant and it’s likely that the infectious period with omicron will be different.
However he added: ‘Nevertheless, this current study reinforces concerns that reducing the self-isolation period to five days will increase the risk of highly infectious people spreading infection as they return to work or school.’
Changes to self-isolation rules came as Covid cases fell once for the eight consecutive day, and NHS hospital admissions remained flat.
A total of 109,133 positive tests were logged across the UK yesterday down 39 per cent on the tally a week ago.
However, deaths — which are a lagging indicator of the outbreak— have been slowly creeping up in recent days, with 335 more victims registered.
Meanwhile, the latest hospital data shows there were 2,184 admissions for virus-infected patients on January 9, up 5 per cent compared to the previous. Daily admissions have fallen on three of the past seven days.
NHS leaders have publicly voiced optimism that Omicron-fuelled pressure on hospitals has already peaked and that eight new Nightingale surge hubs will not be needed.
