omicron wave: cutting isolation period makes no sense

On the other side of the Atlantic, the US Centers for Disease Control and Prevention said they are changing the self-isolation period to five days, given what is known about the Omicron version.

Now, Health Secretary Sajid Javid has announced that the self-isolation period for people who test positive for COVID in England is being cut to a full five days (it is not clear, at this point, if the UK Other nations will do the same).

From Monday, 17 January, people in England will be able to leave isolation for five days after two negative lateral flow tests (24 hours apart).

The rules are the same regardless of vaccine status. As a medical microbiologist, I am concerned that there is little scientific evidence to justify the safety of these reduced measures.

Some argue that Omicron is “mild” and does not result in an increase in the number of hospitalizations, but it should be remembered that this wave corresponds to the considerable level of protection achieved by a combination of natural infection and vaccination-induced immunity. Along with spreading in the population.

Instead, the greater impact – certainly in the UK – appears to be absenteeism resulting in many essential services struggling to function. So have we seen economic drivers overtake the scientific justification of COVID management plans?

Let’s consider the scientific justification for recommended isolation periods. A comprehensive UK-based systematic review of 79 papers from around the world (excluding those with very low case numbers) reviewed the viral shedding of 5,340 infected people.

It evaluated not only the viral load determined by PCR testing, which can remain positive for some time beyond clinical recovery, but also the ability to produce viable virus from these people, meaning they are still clearly were infectious.

The review showed a low viral load in the first few days, but then a peak around days three to six, tapering off in seven to nine days until no viable virus could be recovered by day ten. In other words, the data supported a ten-day isolation period.

Some studies have suggested a slightly shorter duration of viral shedding in people with no symptoms, but decisions on national policy should be based on all infections, not just a sub-set.

A more recent preprint from Japan (a study that has not yet been published in a scientific journal) looked at the viral shedding attributed to omicrons. The study mirrored the findings of a systematic review, showing that viral shedding is highest three to six days after the onset of symptoms.

And a small study from the University of Exeter, published on the same day as Javid’s announcement, found that one in three people are still potentially contagious after five days.

Evidence suggests that in five days many people will still be shedding viable virus, potentially resulting in a much further spread of COVID. So what evidence is the government using on which the recent cut in isolation periods is based?

social and economic pressure

Lateral flow tests are a quick and practical way of assessing infectivity, but these tests are done in-house and may not always be performed to stringent criteria, which means they can give false results.

Correctly taking a swab sample is important for the performance of the test, and it requires the examiner to report the test result appropriately. Many social or economic pressures can lead testers to compromise testing and reporting protocols.

Reducing the isolation period to five days risks leaving infected people back in the community at their peak times for the spread of the infectious virus.

This is both silly and dangerous to those around them. People want to feel safe when they go out, knowing that others are getting tested correctly and being isolated until they become a risk to others.

I urge our policy makers to look at scientific data and draw a sensible, informed, correct conclusion.

by Sally Cutler, Professor, Medical Microbiology, University of East London