Cutting the quarantine period for people who have been in contact with an infected person to one week and requiring them to test negative on the last day would be just as effective as the existing government advice of 14 days, a study claims.
Currently, a person who tests positive for coronavirus is told to self-isolate for two weeks, as are people they may have come into contact with.
But researchers from the London School of Hygiene and Tropical Medicine created a computer model to see how reducing the quarantine period for contacts affected the spread of the virus.
The findings indicate that contacts who test negative after seven days of quarantine are unlikely to be infectious and can be released with little risk.
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Cutting the quarantine period for people who have been in contact with an infected person to one week and requiring them to test negative on the last day would be just as effective as the existing government advice of 14 days, a study claims (stock)
In the new study, published in The Lancet Public Health, researchers used mathematical modelling to estimate the effect of different quarantine and testing strategies on reducing onward transmission of the virus.
Using data from Public Health England (PHE) and NHS England, the researchers simulated the levels of virus an infected person would be likely to produce at each stage of infection, alongside timing of symptom onset and test sensitivity.
Within the computer model the scientists found 59 per cent of onward coronavirus transmission is prevented with a 14-day quarantine for close contacts.
This is based on the assumption that two out of three people who are told they need to self-isolate actually do so, what the researchers call 'moderate adherence'.
If the same level of adherence was applied to a seven-day isolation window with a PCR test at the end of the week, the model predicts the impact on onward transmission to be roughly the same, at 54 per cent.
Using a lateral flow test instead would result in an effectiveness of 50 per cent, the authors found.
This figure is based on the assumption the lateral flow tests detect 76.8 per cent of cases, in line with if they are administered by a healthcare professional.
But when using the accuracy level of 48.9 per cent, as was found from the Liverpool trial, the figure drops to 44 per cent.
|Protocol||impact on transmission|
|7-day quarantine with a PCR test on last day||54%|
|7-day quarantine with a lateral flow test on last day (upper estimate)||50%|
|7-day quarantine with a lateral flow test on last day (lower estimate)||44%|
|5 consecutive days post-exposure of lateral flow tests||43%|
Pictured, a lorry driver in France getting a lateral flow test to screen for Covid-19
Rapid lateral flow Covid tests 'do more harm than good'
Boris Johnson's extortionate Operation Moonshot mass-swabbing scheme could accelerate Covid's spread because the tests are so inaccurate, a top expert has warned.
Professor Jon Deeks, a testing expert at the University of Birmingham, accused the Government of making lateral flow tests seem 'better than they are' in a bid to justify the £100billion scheme.
Professor Deeks and other scientists are concerned that the tests are significantly less accurate when people do them themselves, as is the plan for Operation Mooonshot.
A trial of one test used by the Government found that it detected 79 per cent of coronavirus cases when administered by a trained professional but only 40 per cent in a real-world self-swabbing scenario. This is significantly lower than the more expensive but slower PCR tests which detect 70 to 99 per cent of positive cases.
Despite concerns about their reliability, the 15-minute tests – which the UK has spent more than £1billion on – are being offered to councils across England to be used as self-tests in schools, universities, care homes and in critical businesses to keep the country ticking over until everyone is vaccinated.
Over the weekend Business Secretary Alok Sharma suggested the rapid tests had the potential to make workplaces 'completely safe', while Matt Hancock claimed the quick tests had 'been hugely successful in finding positive cases quickly'.
But Professor Deeks warned the tests missed 60 per cent of infected people in a mass trial in Liverpool when people swabbed themselves, a statistic which he feels is not being communicated to the public. He told Sky News: 'Government messaging on this hasn't been explaining this to people and it's a bit difficult. Most of us have never done a diagnostic test in our lives ourselves, and we would expect a positive to mean 'yes' and a negative to mean 'no'.
But the model also found quarantine could be replaced entirely by daily testing with lateral flow kits for the first five days after exposure.
These tests are far less accurate than lab-based PCR tests and have been found to identify as few as 79 per cent of coronavirus cases when administered by a trained professional but only 40 per cent in a real-world self-swabbing scenario.
However, repeated testing over time increases their accuracy, experts say.
In the model, taking a lateral flow test for the first five days would prevent 43 per cent of transmission events, the study suggests.
Dr Alexander Edwards from the University of Reading, said: 'The maths of diagnostics is unfortunately not very intuitive.
'For example, if a test is only able to detect virus half of the time, you might think an easy improvement is to just test twice. But unfortunately testing twice doesn’t really “double the accuracy”.
'On the other hand, if you have access to inexpensive quick lateral flow tests, maybe using multiple tests in a carefully designed system could give the same benefit as using a single expensive and slow test.'
The authors stress that people should continue to observe the official guidance on quarantine and self-isolation, which the UK Government has set at ten days, until their findings can be verified with further research based on real-world data.
Assistant Professor Sam Clifford, joint-lead author of the study, says: 'Adherence to quarantine rules is key for reducing onward COVID-19 transmission.
'Our findings suggest that incorporating testing of contacts into a trace-isolate system could potentially help to reduce quarantine times, and this in turn may improve adherence by making it easier to complete the full isolation period.
'Our study did not evaluate costs, however, and further studies are needed to address this, as well as to further verify our findings.
'A large component of the effect of any strategy we modelled was that of strict isolation upon the onset of COVID symptoms, which should be followed at any point after exposure, including after the end of the specified quarantine period or after negative test results.
'We recommend people continue to follow the official guidance on quarantine and self-isolation, which will give us the best chance of bringing this virus under control while vaccination continues.'
HOW LATERAL FLOW TESTS ARE ONLY TRUSTWORTHY WHEN ADMINISTERED BY TRAINED STAFF
Lateral flow tests are only accurate at diagnosing coronavirus when administered by trained professionals, studies have repeatedly shown.
The tests, which give results in as little as 15 minutes, use swabs of the nose or throat. Samples are then mixed in a testing liquid and put into a plastic cassette which can detect the presence or absence of coronavirus and then produce an image of a line, the same way as a pregnancy test, to indicate whether it is positive or negative.
The Department of Health and NHS are instructing people to use the tests on themselves, despite manufacturers of some kits saying they shouldn't be used as DIY swabs.
Both the swabbing procedure and the use of the test cassette can easily be done wrong and affect the accuracy of the test.
If the swab isn't done for long enough, or deep enough into the nose or throat, it may not pick up fragments of virus. Medical professionals are also able to use nasopharyngeal swabs, which go right to the back of the nostril, whereas this is not advised for people who test themselves.
And if the sample isn't properly inserted into the cassette the result might be wrong, or people may misread the display when it produces a result.
SELF-TESTING CUT ACCURACY FROM 79% TO 58%
A University of Oxford and Public Health England evaluation of the Innova lateral flow test, which is being widely used in the UK, found its sensitivity - the proportion of positive cases it detected - fell from 79 per cent to 58 per cent when it was used by untrained members of the public instead of lab experts.
Based on this evaluation, officials pushed ahead and used it for a real-world self-testing trial.
PILOT IN LIVERPOOL FOUND FEWER THAN HALF OF POSITIVES
When the same Innova test was trialled on members of the public in Liverpool - with people taking their own swabs and trained military staff operating the tests - the swabs picked up just 40 per cent of positive cases.
In the study the rapid tests detected 891 positive results, compared to lab-based PCR swabs that found 2,829 positives in the same group. This means 1,938 people got a wrong negative result from the rapid test.
The study didn't compare this to professionally done rapid tests, but the manufacturer Innova claims its test is 95 per cent sensitive in lab conditions.
...BUT TESTING DONE BY MEDICS IN SLOVAKIA 'REDUCED INFECTIONS'
Despite rapid lateral flow tests getting bad press, officials in Slovakia used them on 5.2million people - almost the entire population of 5.5m - in a trial that a study later estimated to have cut the country's infection rate by 60 per cent.
The tests used were between 70 and 90 per cent accurate and all the swabs and evaluations were carried out by trained medical workers. They used deep nasopharyngeal swabs, that go to the back of the nose, whereas self-testing generally relies on a swab of only the nostril.
London School of Hygiene & Tropical Medicine researchers said that the scheme successfully weeded out coronavirus cases that wouldn't have been found otherwise, slashing the number of cases by over half in a week during a lockdown.
HOW RAPID TESTS ARE DIFFERENT TO LAB-BASED PCR SWABS
Lateral flow tests are an alternative to the gold standard PCR test - known scientifically as polymerase chain reaction testing - which is more expensive and more labour-intensive but more accurate.
PCR tests also use a swab but this is then processed using high-tech laboratory equipment to analyse the genetic sequence of the sample to see if any of it matches the genes of coronavirus.
This is a much more long-winded and expensive process, involving multiple types of trained staff, and the analysis process can take hours, with the whole process from swab to someone receiving their result taking days.
It is significantly more accurate, however. In ideal conditions the tests are almost 100 per cent accurate at spotting the virus, although this may be more like 70 per cent in the real world.