Drop in test sensitivity may be especially significant for omicron variant, which is thought to first replicate in the throat

Lateral flows tests are poorer at detecting coronavirus if users only swab their nose, results show. Since last summer, the Government has been providing test kits that no longer require people to swab their tonsils. But in recent months, many people have reported that they have tested negative if only swabbing their nose, but positive if they include a throat sample. The Telegraph has seen data published by the Department of Health and Social Care (DHSC) which shows that, for the popular Orient Gene test, test sensitivity falls if the throat is not swabbed. For high viral loads, the test picks up 92 per cent of cases with nose and throat but only 88 per cent with nose alone. For lower viral loads, it detects just 47 per cent of cases compared with 59 per cent if both are carried out. In its report, the DHSC concluded that the drop in detection was acceptable because it would make the test more tolerable for people having to test on a daily or weekly basis. “Moving from throat-and-nose swab to anterior nares swabbing results in a reduction in test sensitivity across all viral loads,” the report concluded. “However, in light of the likely improved tolerability from users of anterior nares swabbing, especially for a daily and or weekly testing context, this reduction is deemed acceptable.”

Experts are increasingly warning people to swab both the throat and mouth, even if their testing kit tells them not to. Professor Tim Spector, lead scientist on the Zoe Covid study, said recently: “Always swab both your throat as well as your nose if you want an accurate LFT.” Professor Jennifer Rhon, a cell biologist at University College London (UCL), recently posted a photo of a positive lateral flow test on Twitter, warning that she had repeatedly tested negative when using just a nose swab. She said: “Today, with the wrong symptoms and after a string of negative LFTs, I finally took Twitter advice and swabbed my throat as well as my nose. If you think you might have Covid, consider adding the throat sample.” Prof Irene Petersen, an epidemiologist at UCL, has speculated that nasal swabs may be less effective at picking up a positive omicron infection because the virus may first replicate in the throat before moving to the nose. Many people have reported sore throats as an early symptom of the variant. Prof Peterson said that to detect an infection as early as possible people should swab their throat as well as their nose, even if the instructions suggested otherwise.

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