Rapid tests (aka: Antigen tests, or lateral flow tests) are high specificity, low sensitivity tests. That means they’re biased towards the negative side: they’

Rapid tests (aka: Antigen tests, or lateral flow tests) are high specificity, low sensitivity tests. That means they’re biased towards the negative side: they’re unlikely to return false positives, but quite likely to give false negatives. Such tests are useful for epidemiological studies, or for answering the “do I have Covid antibodies?” question. But they’re not a reliable way to actually test for Covid. You need a PCR test for that!