New rapid Covid tests missed more than 50% of cases in UK trial - how do they work?

New rapid coronavirus tests being trialled in Greater Manchester missed more than 50 per cent of positive cases, according to reports. It was hoped the tests would provide a quick and easy way to find out if people had the virus, with results available in around 20 minutes However, in a letter seen by The Guardian, scientists working on Greater Manchester’s mass testing expert group (MTEG) expressed concerns about the accuracy and sensitivity of the tests. Is the test effective? The test, which is part of the government’s mass-testing strategy, known as Operation Moonshot, only identified 46.7 per cent of infections during the trial in Manchester and Salford last month, according to the Guardian. Scientists have said they have “significant concerns” after data from the North West pilot showed low sensitivity for detecting Covid. They said: “MTEG have significant concerns and do not feel the data supported the investment in the large scale rollout of Direct RT-Lamp saliva testing in any of the proposed clinical settings considered (hospital staff, care staff, community settings) at this time.” The government has disputed the claim that the tests are inaccurate, with the Department of Health and Social Care (DHSC) saying that results from three other trials demonstrate their effectiveness. However this data is not publicly available. Co-chair of DHSC’s Technical Validation Group, Professor Mark WIlcox, argued that the tests have been proven “in other laboratories” and it is “incorrect to claim the tests have a low sensitivity”. He said: “The direct LAMP tests used in Manchester have been validated in other laboratories and in real-world testing for use in different settings. “It is incorrect to claim the tests have a low sensitivity, with a recent pilot showing overall technical sensitivity of nearly 80 per cent rising to over 96 per cent in individuals with a higher viral load, making it important for detecting individuals in the infectious stage.” How do the tests work? The tests are manufactured by British firm OptiGene, with the government paying £323m for 90 million testing kits and other equipment needed to process them. One version of the test, the Direct RT-Lamp, requires a saliva sample to be heated for safety, then it is added to the machine which can detect the virus. The second type, the RNA lamp, requires longer to produce a result, as it involves the extraction of nucleic acid from the sample. What about the trial in Liverpool? The government launched another testing trial in Liverpool this month, which involves a new type of saliva test to be offered to everyone in the pilot area. Concerns have been raised, as the instructions for the saliva tests say “negative results do not rule out” infection. It also states that the tests should not be used for treatment decisions or “infection control decisions”.