Its not even Omicron. Rapid tests always had something like a 40% false-negative rate or something stupidly high.
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That's why you're supposed to take two tests if you're asymptomatic, to reduce the chances of a false-negative.
Fortunately, the false-positive rate is less than 5% IIRC, and fairly reliable.
EDIT: Sensitivity and Selectivity isn't really false-negatives or false-positives. But for the purposes of this discussion, its probably good enough. Besides, I'm just an ignorant programmer who doesn't know the difference between them.
https://www.bizpacreview.com/2021/12/29/fda-says-rapid-at-ho...
“RADx recently performed preliminary studies evaluating the performance of some antigen tests using patient samples containing live virus, which represents the best way to evaluate true test performance in the short-term. Early data suggests that antigen tests do detect the omicron variant but may have reduced sensitivity,” according to the FDA.
Frankly, going from 60% to 40% doesn't change my viewpoint on rapid tests. Its all "unreliable false negative" to me (I don't know what it is for Omicron, I'm just pulling 40% out of nowhere). But whatever it was, the sensitivty was always so low that you never could rely upon a negative-reading, due to the high chance of false-negatives.
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Rapid tests remain useful, but you _MUST_ always be mindful of their high false negative rate. The fact that their "unreliable stat got even more unreliable" isn't really news, because you shouldn't have been relying upon it anyway.
If you test positive, you're supposed to stay home and isolate so you don't spread COVID.
Tests aren't perfect, since as you said, there seems to be a significant false-negative rate with Omicron, and you can be contagious before you show symptoms, but the tests help prevent people from spreading confirmed cases, and can be helpful to pre-test before you spend time with someone who is at high risk for COVID.