It's about the testing we do with something called PCR, an amplification technique, better known to biologists as a research tool used in our labs when trying to unpick mechanisms of disease. I was frankly astonished to realize they’re sometimes used in population screening for diseases – astonished because it is a very exacting technique, prone to invisible errors and it’s quite a tall order to get reliable information out of it, especially because of the prodigious amounts of amplification involved in attempting to pick up a strand of viral genetic code. The test cannot distinguish between a living virus and a short strand of RNA from a virus which broke into pieces weeks or months ago.
https://www.algora.com/Algora_blog/2020/10/04/german-corona-investigative-committee