$CODX Sure: Primers (usually two separate pieces of DNA) are combined in a qRT-PCR reaction mixture, along with the patient sample, and polymerase (from bacteria). These primers have been designed to bind to specific sequences of RNA (or DNA). In the case of Covid19, the primers are designed to bind ONLY to the sequences found in this virus' RNA. During qRT-PCR tests, which takes roughly 90-120min, primers are supposed to bind to the virus RNA. Then the bacterial polymerase extends the primers to form a longer DNA chain. However, if there is no viral RNA to bind, the primers can bind to themselves!!! When the bacterial polymerase extends these "primer-dimers", it generates NON-SPECIFIC product, in essence FALSE POSITIVES. In basic terms, Co-primers are bound together at opposite ends and as such cannot form such dimers and subsequent false positives.