this territory is moderated
At least that's what the guy who invented it said.
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PCR detects traces of DNA or RNA. It's used as a proxy. The accuracy is mega high though for a specific target. But viruses are evolving constantly. Within a single person, virus population are very heterogenous. So when the test works, the presence is clear. When it doesn't, there could be variants of the target or no virus at all.
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