What are COVID lateral flow tests and will they help the UK return to normal?

Boris Johnson is reportedly planning to use millions of rapid lateral flow tests to help get the country to a “new normal” when lockdown is eased.

NHS Test and Trace is preparing for a nationwide scheme called “Are you ready? Get testing. Go” that will see more than 400,000 of the 30-minute coronavirus tests sent by post to homes and workplaces every day, The Times reported.

The prime minister will talk about the testing programme on Monday when he announces his plan to ease out of lockdown, with the quick tests a crucial part of returning to everyday life, the report added.

But how do the tests work and how could they be used to help the country after lockdown is eased?

Watch: Oxford professor outlines importance of lateral flow tests for easing lockdown

What are lateral flow tests?

Lateral flow devices are quick-turnaround coronavirus tests that use nose or throat swabs.

The tests are performed without the need for laboratory assessment.

They are less sensitive than PCR (polymerase chain reaction) tests, which are considered the gold standard.

How do they work?

Lateral flow tests work best among those with higher viral loads, where more virus is detected in the nose and throat.

Looking at data from more than a quarter of a million people who have taken part in England’s test and trace scheme, scientists found that the greater the viral load, the more infectious the person.

Applying previous estimates of the sensitivity of four lateral flow devices to those findings, the researchers found that the tests would detect between 83.7% and 90.5% of cases leading to onward transmission.

How are lateral flow tests currently used?

Lateral flow tests have been deployed to councils across England to support community testing efforts for people without symptoms.

Earlier this month, the government said 2.2 million tests had been carried out under the scheme to detect 44,000 positive cases.

The government is making millions of rapid test kits available to the NHS, care home staff, primary care such as GPs, schools, colleges and universities.

Frontline workers, such as police, firefighters, Border Force staff and civil servants working on the COVID-19 response, also already have regular quickfire tests.

Businesses of more than 50 people in England with employees who cannot work from home can also order rapid tests through the government.

What are their limitations?

The British Medical Journal has warned that local authorities using lateral flow tests have not made the limitations clear to the public, including that they don’t identify all infections.

Public Health England has said 23.2% of the tests' results are false negatives, and that their sensitivity was an average of 76.8% but this dropped to 57.5% when used in track and trace centres by self-trained staff.

Jon Deeks, professor of biostatistics at the University of Birmingham, has previously argued that people should not be told that lateral flow tests are “better than they are”.

He said tests in a mass pilot scheme in Liverpool “missed 60% of the cases which would have been picked up by PCR”.

But Professor Louise Kenny at the University of Liverpool said this claim was “factually incorrect” and that the findings from the pilot scheme were misinterpreted.

Speaking on BBC Radio 4’s Today programme, she said: “Much of the confusion in the debate around the accuracy of lateral flow has arisen because their performances are being directly compared with PCR.

“But critically, PCR tests also detect people with really low viral loads who are unlikely to be infectious, so that comparison is really unhelpful and underestimates the effectiveness of lateral flow.”

What do experts say about them?

Prof Deeks claims “untrained people at home” can cause “serious harm” with lateral flow tests, but this has been disputed by scientists including Dr Susan Hopkins, chief medical adviser for NHS Test and Trace, and Professor Calum Semple, from the Scientific Advisory Group for Emergencies.

They stated that Prof Deeks’ BMJ article contained “factual errors" and made "several unsubstantiated allegations and assertions”.

Tim Peto, professor of medicine at the University of Oxford, added: “We know that lateral flow tests are not perfect, but that doesn’t stop them being a game-changer for helping to detect large numbers of infectious cases sufficiently rapidly to prevent further onward spread.”

Lateral flow devices used by the UK government go through a rigorous evaluation by the country’s leading scientists, a Department of Health and Social Care spokesperson said.

What different types of coronavirus tests exist?

There is a range of tests for coronavirus, including the widely used PCR nasal and throat swab tests, which take between 12 and 24 hours to return results.

Other types include loop-mediated isothermal amplification (LAMP) testing, which can return results in as little as two to three hours.

Portable lateral-flow tests can generate results in less than half an hour and do not require a laboratory.

They can be self-administered or done by someone else and can detect coronavirus in people who do not show symptoms.

Watch: What you can and can't do during England's lockdown