Is it time to follow the US five day Covid-19 isolation rule?

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Omicron has had the entire country in its highly infectious grip. An astonishing one in 15 people had the virus in the week before New Year, the Office for National Statistics confirmed on Wednesday. In London, where the outbreak is thought to be two weeks ahead of the rest of the country, it was one in ten.

Despite the spiralling numbers, vaccination means the virus is having a milder impact, in terms of causing ill health, than previous variants.

The most pressing problem now facing health chiefs and policymakers is one of disruption. More than one million people are believed to be currently self-isolating due to a positive Covid diagnosis, which is having a paralysing effect on healthcare, transport, schools, supermarkets and public services such as bin collections.

If this continues, the economic impact will be considerable – not to mention the effect of cancelled operations and hospital treatments as the health service battles under the dual pressure of rising Covid admissions and unprecedented staff absence.

Twenty-four NHS Trusts last week declared critical incidents and patient waiting lists have hit six million, driven not just by Covid itself but due to the fact that vast swathes of the workforce are stuck at home. On Friday, health chiefs warned that hospitals have never known such high staff absences, with 120,000 off work last week – half of them self-isolating or testing positive for Covid – and the Army is now being brought in to plug the gaps.

As countries around the world battle similar problems, the focus has turned to whether the current strict rules on self-isolation are fit for purpose. Reflecting the latest research on how long individuals are likely to remain infectious, experts are looking at whether people could potentially be released from isolation earlier to reduce the amount of time they are off work.

The situation is not being made any easier by the fact that regulations are increasingly complex and confusing to navigate.

In December, in England and Wales, isolation time was cut from ten days to seven – so long as the patient records two negative lateral flow tests, 24 hours apart, on days six and seven.

Critically, the NHS states that isolation begins from the day symptoms first begin – they call this ‘day zero’ – not from when the individual tests positive.

So if someone has been suffering from symptoms for two days (day zero and day one) before taking a test (day two), and the results come back a day after that (day three), they will have four further days of isolation – depending on those two negative lateral flows. If one of the lateral flows is positive, they must stay in isolation until day ten.

Those without symptoms start their isolation clock (day zero) on the day their positive test is taken, which – and only if you’re asymptomatic – now no longer needs to be confirmed with a PCR test, in an attempt to relieve the pressure on testing labs.

The UK’s approach has been followed by both Spain and Ireland, while last week Scotland and France announced similar changes.

Yet some argue these rules don’t go far enough and are undoubtedly leading to people who are no longer infectious or may never have had symptoms having to quarantine for longer than necessary.

A growing number of experts now believe we have reached a tipping point: that the risks to society are so great that the isolation period should be cut to just five days from the onset of symptoms. There is a crucial balance to be struck, they say, between following the science and keeping society functioning.

The US health agency Centers for Disease Control and Prevention (CDC) recently announced that it would slash isolation from ten to five days for people who no longer have symptoms, while here in Europe, Greece is the first nation to adopt a similar policy.

Leading scientists calling for the UK to follow suit – including Professor Tim Spector, the epidemiologist behind the Covid Symptom Study, who said it would ‘protect the economy’.

At present, the Government has ruled it out, saying time is needed to see the effect of cutting isolation from ten days to seven before making any further changes. But could we, as some argue, move to a five-day isolation period now, as America has?

The answer, as ever with this pandemic, is not straightforward.

Some scientists have argued that reducing isolation time to five days from the onset of symptoms could mean people are released while they are still infectious. And this could contribute to a ‘counterproductive’ rise in cases and staff shortages.

Modelling by the UK Health Security Agency, which advises the Government on public health issues, suggests between ten and 30 per cent of people could still spread Covid on day six.

Despite this, Professor Monica Gandhi, a specialist in infectious disease at the University of California, San Francisco, told The Mail on Sunday’s Medical Minefield podcast that she believed the UK should adopt the US rules.

‘The reason that the CDC did this [cut isolation time to five days] is because isolating and quarantine with such a transmissible variant is very disruptive to society. So they are being practical and balancing the fact that it’s an endemic virus with keeping people safe.’

Prof Gandhi, a highly respected trailblazer in HIV research who has also been a vocal commentator during the pandemic, cites a Taiwanese study, the largest contact-tracing study ever performed, which looked at when people passed on the virus after having symptoms.

‘All of it, 100 per cent, occurred in the first five days,’ Dr Gandhi said. ‘Six days or later, there were no transmissions from symptomatic people with Covid to their contacts.’

Prof Gandhi also points out that people with Covid are most infectious before they develop symptoms, which is impossible to control. She said: ‘Two years into the pandemic there’s a realisation it isn’t going to go away. It’s impossible to eradicate. Now we just need to prevent people from getting ill, which vaccination has done.’

One of those in the UK who is in favour of a five-day isolation period is Professor Paul Hunter, an epidemiologist at the University of East Anglia. He explains that most studies have looked at how long people test positive on PCR tests – which varies from about four days before symptoms begin to a few weeks afterwards. But this alone doesn’t prove they are infectious, because people can shed ‘dead’ virus, which can’t replicate in another human body.

‘One of the few studies that has looked at the close contacts of Covid cases found that round about day three, whether or not you still tested positive on a lateral flow, you were very unlikely to infect anybody else.

‘So keeping people off work just because they had a positive test a couple of days ago doesn’t make much sense. There is no doubt the current system is keeping people in isolation who are no longer infectious, or are only very low risk of being infectious.

‘The risk is much greater from those who’ve been infected but don’t yet have symptoms.

‘We should reduce isolation to at least five days, and let people back to work even if they test positive on a lateral flow.’

The same rules could also apply to asymptomatic people, he adds.

The exact number of asymptomatic infections has never been known, but it is thought to be between 20 per cent and one third of the total.

Most are picked up by routine lateral flow tests.

While some go on to develop symptoms, others remain asymptomatic. The evidence suggests that although they can still transmit Covid, it’s about a third less likely than those with symptoms.

‘If we were having this conversation at the start of the pandemic I would be up for keeping everyone in isolation for two weeks,’ Prof Hunter adds. ‘But the difference is that then there was hardly any Covid in the community and a single case getting out could spread rapidly into a population that had no immunity.

‘Now you’re not trying to stop it spreading any more. In terms of the actual impact on transmission, the difference between a five-day isolation or seven will be minimal.’

Lateral flow tests tell us when we’re most infectious, as they pick up proteins associated with live viral cells.

This is why the UK rules required negative tests on days six and seven to leave self-isolation.

But they are not foolproof. Some experts say they can still pick up small amounts of viral protein even when transmission is highly unlikely, either because there are not enough cells to infect another person or the cells are ‘defective’ and no longer live.

Meanwhile, Professor Lawrence Young, a virologist at the University of Warwick, suggests the opposite also may be true, due to the nature of Omicron: ‘It’s possible that Omicron can transmit at much lower viral loads – meaning less of the virus is needed to infect a person than with previous variants.

‘This may give rise to a situation where people are testing negative [on lateral flow tests] due to low levels of the virus in their system, despite being infectious.’

Graham Cooke, Professor of Infectious Disease at Imperial College London, agreed: ‘Omicron might be behaving differently in terms of how much of it you need [in your system] to be infectious.’

Neither Prof Young nor Prof Cooke is in favour of reducing the isolation period as it stands because the incubation period for the virus, and the speed at which the infection progresses varies from person to person.

Both point out that, fundamentally, we still don’t know enough about Omicron’s ‘infectious window’.

Prof Young agrees that most people are probably no longer infectious five days after symptoms begin, but adds: ‘Like everything in biology, it’s not an exact science. So my feeling has always been that seven days gives you a very good margin, to make sure that you are not infectious any longer.’

He does, however, concede that as we understand more about Omicron this may change. ‘If the infectious period is shorter – which may be the case if you are asymptomatic or only have mild symptoms – then reducing the self-isolation period to five days is a possibility,’ he adds.

In America, patients are not required to take a lateral flow test to end isolation, but they are asked to wear a mask for five days when around other people.

None of the UK experts we spoke to supported this. Prof Young said: ‘If we were to cut isolation time to five days, it would require strict enforcement of lateral flow testing before ending isolation and, of course, no problems with the availability of these tests.’

However, Prof Hunter points out that the symptoms of Omicron are generally mild and might go unnoticed for longer before someone seeks out a test.

He adds: ‘In which case there’s even less of an argument for a longer isolation period, because by the time we’ve got our results or thought “Maybe this cold isn’t just a cold”, we might already be past the peak infectious period.’

Seven-day isolation is designed to reduce transmission, but there are now questions as to whether that even remains a good idea at all.

Many people in the UK are protected against severe disease because they are vaccinated – and 60 per cent of the population has now had a booster.

But there is already evidence that immunity from a third shot wanes after ten weeks.

Prof Hunter suggests that slowing the spread of Covid may now actually be a bad idea: ‘Prolonging the peak may just mean that you’re actually infecting more people just as their immunity starts to wane.

‘We’re all going to be infected with Omicron, but ultimately the issue is whether we’re going to get infected at a time when we’re still protected against disease.’