Many question the effectiveness and validity of the PCR test.
There is NO isolated, real-life SARS-CoV-2 specimen.
Mike Adams says that, "All the PCR tests are merely running against digital libraries of base pair sequences which were fraudulently labeled “covid” by the corrupt, criminal CDC and WHO 
It is also difficult to test when "no one has isolated any covid-19 virus from any “infected” human and proven it to be the cause of disease."
... and CDC
Rappoport on self-testing.
... people can remain PCR positive for up to 12 weeks after infection and long after they are transmissible and infectious. Walensky (CDC). https://edition.cnn.com/2021/12/29/health/us-coronanavirus-wednesday/index.html