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Rapid Covid Tests Are More Widely Used: Can They Be Trusted?

December 28, 2020

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Britain and France agreed this week to use on-site Covid-19 rapid tests to end a 48-hour lockdown on travel between the two countries, the latest adoption of a technology that could become a crucial tool to control the spread of the coronavirus in 2021.

The UK government has spent at least £ 1.5 billion on so-called lateral flow tests and has already supplied the simple devices to local authorities, nursing homes, hospitals and universities. The British regulator went further on Tuesday, giving the tests a emergency clearance for use by members of the public without medical training.

Supporters of lateral flow testing say the devices, which can provide a result in 20 minutes, will significantly increase the UK’s testing capacity and are a useful tool in finding people who are currently infectious. From next month, tests will be rolled out to UK schools to identify cases of the virus before the start of the new term.

“Testing asymptomatic people is a huge priority,” said John Bell, Regius professor of medicine at the University of Oxford, who has overseen studies on the accuracy of these tests for the government. “If there isn’t a test, they don’t get caught. Every positive result you get is a victory. “

But several scientists remained skeptical despite the regulator’s approval and its growing adoption, arguing that the public has been misled about the accuracy of the tests.

contrary to RT-PCR tests, which looks for the genetic material of Covid-19, lateral flow tests identify a protein antigen on the surface of the virus. Lateral flow devices do not amplify the virus (unlike RT-PCR tests) and therefore struggle to detect lower levels of infection.

Several analyzes have shown that the lateral flow test developed by Innova – the UK’s largest supplier and one of the few tests meeting the government’s precision criteria – has resumed less than half active infections.

“Schools are going to be a nightmare,” said Tom Lewis, clinical manager of pathology at North Devon District Hospital. “If you rely on that to collect the stuff, you’re going to miss more than half of it.”

Oxford University professor Tim Peto disagreed. “They’re not perfect, but that doesn’t stop them from being a game-changer to help detect cases of infectious diseases,” said Professor Peto, who worked with Professor Bell to validate the accuracy of the tests.

Their analysis found that the Innova tests detect between 84 and 96 percent of infections in people with high viral loads, making it ideal for identifying people who are currently infectious. The study also concluded that using the devices to identify and then quarantine cases of Covid-19 can reduce transmission by 67 to 90%.

This means that the test is the most effective at catching infectious people and less effective at identifying people who have a low viral load, who are normally at the start or end of their Covid-19 infection. On the other hand, the Gold standard PCR tests detect all forms of viruses.

The best source of data for widespread use of rapid tests to trace infection and reduce transmission comes from Slovakia, where two thirds of the population – 3.6 million people – were tested between October 31 and November 1 and more than 57,000 cases have been identified.

Using lateral flow testing to identify and quarantine cases is estimated to reduce transmission of Covid-19 by 67-90% © Matthew Horwood / Getty

Analysis campaign by researchers at the London School of Hygiene and Tropical Medicine estimated that the mass testing regimen, coupled with quarantine measures, led to a 60 to 70 percent reduction in the rate of infection in Slovakia.

“We are seeing strong evidence that the combination of short lockout and mass testing led to a very rapid reduction in the burden of Covid-19,” said Stefan Flasche, professor of vaccine epidemiology at LSHTM and co- author of the article.

The largest pilot program in the UK was conducted in Liverpool, where 25% of the city’s 497,000 residents took a rapid test in November, leading to the identification of 897 positive cases, according to full data released Wednesday. The Innova tests used detected 40% of PCR positive cases, with two thirds of those detected having a high viral load.

The academics who led the study said targeted rapid testing was both popular and valuable. Although they could not prove that the tests led to a drop in the infection rate, they did note that the cases in Liverpool fell faster than Manchester neighbor.

Evidence suggesting that lateral flow tests are able to detect the virus when carriers are infectious suggests they may be particularly useful in making short-term behavioral decisions, such as entering a nursing home to visit a relative. . However, scientists widely agree that some pre-symptomatic cases will be missed, making it an imperfect tool.

“There is no perfect test, that’s the problem, everything is a compromise,” said Jo Martin, professor of pathology at Queen Mary University. “You have to know its limits when you take it.”