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Mass coronavirus testing for people without symptoms will be rolled out across England from this week. Public health officials hope that rapid and regular tests will help to identify people who have caught the virus but not fallen ill, so they can self-isolate before they spread the disease.
Where will tests happen?
All 317 local authorities in England are eventually expected to offer mass testing. So far, 131 have signed up with 107 already performing tests in the community. Authorities such as Milton Keynes and Essex are focusing their tests on key workers and people who need to leave home for essential reasons. Further testing is being rolled out at major businesses.
How do the tests work?
Lateral flow tests have a strip of antibodies that bind to coronavirus. When a nasal swab is tested in the device, any virus in the sample sticks to the antibodies and shows up as a dark band or fluorescent glow on the test strip.
How good are they?
Lateral flow tests have pros and cons. The main advantages are that they are cheap, deliver fast results – within 30 minutes – and do not need to be processed in a laboratory. The downside is they are less accurate than the gold-standard PCR lab tests. In a trial in Liverpool, lateral flow tests missed more than half of asymptomatic cases, and 30% of symptomless people with high viral loads. This means that a person with a negative result may still be infected. Positive test results are far more reliable.
Will the tests help to contain the outbreak?
Using lateral flow tests to detect asymptomatic cases in the community is controversial and scientists are divided over the issue. Many researchers argue that even though the tests miss many cases, they can still reduce the number of people who are walking around and spreading the virus without knowing they are infected. Studies suggest one in three people with Covid-19 do not develop symptoms. The Liverpool trial found more than 3,000 asymptomatic people between November and December who were immediately told to self-isolate. How many would have developed symptoms later and been detected by routine NHS testing is unclear. Another concern is that the performance of the test drops when performed by less well-trained people.
Lawrence Young, a professor of molecular oncology at Warwick Medical School, welcomed more mass testing and said should it be targeted at those who cannot work from home. But he added that repeat testing was essential given concerns over the accuracy of the tests and that levels of virus vary over the course of the disease.
Jon Deeks, professor of biostatistics at the University of Birmingham, believes that nationwide mass testing risks making the epidemic worse because people get the wrong message from a negative test. “When you get a test result stating that you are free of disease people naturally feel safe and relax,” he said. “With the Innova test this is false reassurance.”
Should the messaging be changed?
Adam Finn, a professor of paediatrics at Bristol University, said lateral flow tests must be seen as “red light tests” not “green light tests”. A positive test is a red light, meaning a person has the virus and must self-isolate. A negative test is not a green light, because the person may still be infected, he said.
Susan Michie, professor of health psychology at UCL, and one of the government’s behavioural science advisors, said the tests must be done repeatedly and with a guarantee to support those who test positive and self-isolate. The Liverpool trial found that some of the most disadvantaged communities avoided mass testing, perhaps because of the £10,000 fine they would face if the need to work meant they were unable to isolate.
Source: The Guardian
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