“To vaccinate or not to vaccinate, that is the question”, soliloquised Piglet, “since all vaccines are equal, but some vaccines are more equal than others” – poetic licence applied with apologies to William Shakespeare...
(Eshan Dias' explanation of the process of testing for Covid-19 uses some scientific terminology, but well worth a read for understanding how the PCR test works - or doesn't, as the case may be...