COVID Tests- Why the PCR is better than a Rapid Test

“A negative PCR test needed within 72 hours of boarding a plane…"

If you’re no stranger to traveling, you’ve heard the classic “negative PCR test” requirement needed to enter Taiwan within a set number of hours. Many of us coming from abroad find obtaining a Rapid COVID test at the local pharmacy as easy as counting 1... 2… 3… but a PCR test- that’s a whole other story!

Not only are they expensive, but they take up to 5 days (at least in the pre-2021 era), and who has that time to wait when your plane ticket is on the line?

Still, let’s break down with science why these tests are “better” for air travel and why your money is perhaps worth it for your mental sanity on a plane.

Viruses, such as COVID, are just proteins and DNA. DNA or deoxyribonucleic acid has the code to your human body and everything in it. Basically, it is a blueprint of how to make all the structures of your body (your hair color, eye color, even if you’re tall or short). Viruses aren’t living things (Koonin).

Crazy right- something like a robot can basically change the lives of the human population on a global scale. If you are a Christian, talk about the negative effects of a sinful, fallen world ruining our lives!

Well, if you have a little COVID virus sitting on the surface of a non-living thing, like a desk, it can’t do anything. It’s not living. Eventually, it will die on its own or if you spray it with some alcohol or even if the sun’s UV zaps it, poof- it will degrade. The catch is, if, somehow, it enters your body; you have cells which are living things. The whole purpose of a virus’ existence is to enter a living cell, hijack all its machinery (the stuff that takes DNA and turns it into structures like protein), and make more viruses to eventually have an army that invades the body (Drexler M).

How does this Trojan horse infiltrate? The virus tricks your cell into thinking it is a fellow cell and basically injects its DNA into your body’s cells. Then using the cell’s machinery, the virus produces more baby viruses that become adults who go and infect more cells. The cycle continues until your body is infested with viruses. That’s why if you get infected with one little virus, it takes up to “14 days” for your body to show symptoms of the disease. It takes a while to produce billions of this non-living army (Drexler M).

PCR stands for Polymerase Chain Reaction. DNA is tiny so if you only have one little virus DNA and you try to test for COVID, you won’t get a result even though you’re positive. There’s not enough virus to become an “infection” yet and that’s how viruses get away with hiding from white blood cells initially. Still, if you have a virus and it leaves behind its DNA fingerprint on a PCR test collection, running that sample through a polymerase chain reaction can take that tiny little amount of DNA and make billions of copies of it (“Polymerase Chain Reaction (PCR) Fact Sheet.”)!

What exactly happens when you spit into a vial or when the doctors jam a 15-centimeter swab into your brain through your nose to get some mucus samples? The resulting extraction is your DNA (and any virus DNA)! If you’ve been infected with a few viruses, PCR makes billions of copies of the virus’ DNA in a matter of 6 hours to 5 days. That way, you can tell if you have been infected recently versus waiting up to 14 days to have billions of viruses made and start showing infection symptoms (Jawerth).

A Rapid Test uses something called ELISA or Enzyme-Linked Immunosorbent Assay to test for COVID. How it works is it tests for specific features of COVID. Some tests can test for Antigens or protein spikes from the COVID virus. Other tests can test for antibodies produced in response to COVID from your own white blood cells in the immune system. There’s a strip of absorbent paper that has little antibodies engineered onto it which will attach onto either the antibodies or antigens that match it perfectly, like a puzzle. Everything else gets ignored (Horlock).

Once you pour the liquid of your mucus samples on one end of the strip, the paper soaks it upwards, like coffee filter paper. As it pulls the liquid up, if you have COVID, the antibodies will attach to the COVID material which will cause a color reaction resulting in a “positive” line that you see on one side. If there’s no positive line but only a test line, that means the test worked but there are no COVID parts in your sample.

If this test detects COVID, then why would a flight attendant take one look at it and deny you entry on a plane to Taiwan? Think about it- to get that full line, you’ll need quite a bit of antigens (meaning TONs of COVID spikes) or several antibodies (which or only produced after you’ve been exposed to COVID for quite some time). If you’ve only just been infected by one COVID virus, can this Rapid test detect it? No way, Jose. Try taking the Rapid test a week or two later and you might find that you’re super positive.

Therefore, why can you be assured that a plane with 100% PCR tested passengers puts you in better hands than 100% Rapid tested passengers? It’s likely they were negative at the time they were tested for the virus. Now of course they could have been infected within that 48-72 hours between testing and the plane ride but at least you know they weren’t incubating the virus for 1 or 2 weeks with something like the Rapid test. This is not a plug to say that all planes are COVID free but scientifically you can calculate the probability would be pretty low on a plane full of PCR-negative tested people. Learn science, travel safe!