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People with COVID-19 symptoms who initially test negative on a rapid antigen test (RAT) should test again 1 to 2 days later because RATs are at their most sensitive 4 days after symptoms start, according to US research. The study compared the PCR and RAT results of over 200 adults and kids and found that, over the whole infectious period, the RATs picked up an average of 64 per cent of the PCR confirmed COVID cases. But four days after symptoms began, the sensitivity of the tests peaked and they picked up 77 per cent of COVID cases. The study also found that doing a second test 1 to 2 days after an initial negative test helped to increase the number of cases picked up by RATs.
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