Gates Package — page 944

process cheaper and simpler--and therefore easier to implement at the scale that will be necessary--so let's go through the state of play and see what's in the offing. Since the beginning of COVID, the U.S. government alone has approved more than 400 tests and kits for collecting samples. The one you might be most familiar with--the one that used to require the brain-tickling stick--is a PCR test, and it's the gold standard of diagnostics. If you've got a COVID infection, the virus will be in your airways and in your saliva, and the swab will catch a sample of it. To analyze your swab, a lab technician will add to your sample some specially designed DNA, which makes extra copies of any genetic material from the virus. This step ensures that if there's even a small amount of virus in the sample, it won't escape detection. (It is this process of duplication, which mimics the way nature copies DNA, that gives the polymerase chain reaction its name.) Then a dye is added, and if the viral genes are present, the dye will begin to glow. No glow, no virus. Creating a PCR test for a new pathogen is a pretty easy task once you've sequenced its genome. Because you already know what its genes look like, you can create the special DNA, dye, and other necessary products very quickly--which is why researchers were able to establish PCR tests for COVID just 12 days after the first genome sequences were published.6 Unless the sample is contaminated, a PCR test is unlikely to give you a false positive--if the result says you're infected, you almost certainly are--but sometimes it can return a false negative, meaning that it says you're free and clear even though you're not. This is why if you're experiencing symptoms and get a negative PCR test, you may be asked to take the test again. The test may also pick up on genetic bits of the virus that remain in your blood or nose long after you've been sick, so you may test PCR-positive even if you're not infectious anymore.