COVID: why are people testing positive on lateral flow tests then negative on PCR?

In the UK over the last few weeks, there have been a growing number of reports of people testing positive for COVID on a lateral flow test (LFT) but then negative on a polymerase chain reaction (PCR) test. This stands out because we’ve been led to believe that PCR tests are the “gold standard” and LFTs are crude mass-testing devices – that PCRs should pick up cases LFTs miss, not the other way around.

A number of explanations have been put forward. Some have suggested a faulty batch…

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