Testing for Covid explained

Why fewer people are sick with Covid, even though case numbers are rising: imperfect testing.

Business Insider

The number of Covid-19 deaths are falling. Yet the media keep instilling fear in us with ever rising case numbers. I hope the fact that case numbers are rising, yet fewer people are sick, makes you stop and think. The following explains why the numbers are seemingly contradictory.

The explanation lies in how testing for coronavirus happens. A laboratory method called PCR is used, that stands for polymerase chain reaction. The Mayo clinic put together a page explaining what PCR testing is, but I’ll go ahead and briefly summarise the process, in a more simplified way.

A PCR reaction looks for traces of genetic material (DNA) and then amplifies those traces by multiplying them. We have identified the genetic sequence, i.e. the blueprint, of coronavirus Sars-CoV-2, which means we know exactly what it looks like. When your throat is swabbed or blood is taken from you, the PCR test is then used to look for specific parts of the coronavirus sequence in the samples taken from your body. I do not want to go too much into details of how DNA and PCR tests are built — suffice it to say that because we know what the coronavirus looks like, we can add elements to our PCR test that attract genetic bits that are specific to the coronavirus we’re after. This means, that if the virus, or elements of the virus, are present in your swab or blood, the PCR test can pick them up and therefore give you a “positive” diagnosis. These bits might, however, be so small that we cannot see them, if we just attract them and then end our test. That’s where the “chain reaction” comes into play. The small parts that we have attracted are then multiplied over and over so that when we eventually visualise our test results, we can see them.

This testing method is, however, so precise and sensitive that it can pick up parts of the coronavirus DNA, even when the virus is already dead. And even if there are only small traces of the virus in your body, because we multiply them over and over in the PCR, it might look like there is a lot of virus. For example, if you have an immune reaction to the coronavirus, i.e. your body is doing everything right and destroying the virus inside you, what will be left is debris of the virus — tiny shattered parts of the virus that was destroyed by your immune system. This debris can be in your body for quite a while and therefore a coronavirus test will come back “positive” even if the virus was long killed in your body. There is very, very likely that this is what’s happening right now and it explains why more and more people test positive for the virus, while actual cases of sickness and death are dropping.

There is strong evidence that there is immunity specific to Sars-CoV-2 and also some prior “base” immunity in the population to Sars-CoV-2*, because it is similar to other coronaviri and regular cold viri that have already circulated through the population for years. So your immune system recognises the threat and attacks the virus. And this increased immunity explains to a large extent why we’re seeing more and more positive results — people are becoming immune, but the PCR tests cannot distinguish between a virus that is alive and one that has already been destroyed.

This has important implications for countries that do tracing, for example, because a positive result does not necessarily mean that the “positive” person can infect others. If their immune system has already killed the virus, they are not infectious, but they are currently still designated an “active case”. It is also a huge problem with media reporting and continued lockdown measures, because essentially the “positive” case numbers are meaningless. We need to look at rates of actual sickness and death and those are clearly dropping, therefore suggesting that “positive” patients are not really sick, i.e. they are immune.

I want to draw special attention to how the media is dealing with this based on the example of the 200 or so Koreans that supposedly got re-infected with the virus after they already had it. That led to claims that there was no immunity against this virus. It made huge headlines and it was particularly worrying, because even the WHO subscribed to that claim. It was as if top scientist in the world didn’t understand their own testing methods and clueless media just kept parotting false claims. The mistake was later explained, but as always, the scaremongering headlines were much bigger and the subsequent explanation of the false test results gained much less traction.

I cannot expect every citizen to become an expert in all the sciences that go into tackling something like a pandemic, but I appeal to fellow scientists and governments to make sure they have all the information before making ludicrous statements and I urge media to be more careful and responsible with what they publish.

*The important finding in the study linked above is that that in 34 % of people in Berlin who had never been in contact with the Sars-CoV-2 virus showed nonetheless T-cell immunity against it (T-cells are part of our immune response against a virus). This means that our T-cells, i.e. white blood cells, detect common structures appearing on Sars-CoV-2 and regular cold viri and therefore combat both of them. Ultimately, this also leads to the conclusion that Sars-CoV-2 is not “novel” at all, which we might have suspected already, when it was named similarly to Sars-1 of which we had an outbreak in 2002–2004.

The other test you have likely heard about is an antibody test. The antibody test is to see whether you had Covid-19 — with this test we’re not looking for the virus, but for cells in your body that you have developed while/after successfully recovering from Covid-19. They mean that you are now protected against the virus in the future.

I mention the antibody test in conjunction with the problematic claim that Sars-Cov-2 is a “novel” virus, which suggests that the population could not have any prior immunity to this virus. Which is what ultimately led to the apocalyptic models that unnecessarily scared the shit out of everyone and caused governments to overreact with their measures.

The Covid-19 antibody tests also react to Sars-1 and even Mers, therefore clearly indicating that Sars-Cov-2 is not novel, but merely a mutation, i.e. it has elements in common with previous viri. The fact that there are similarities and the antibodies in your body recognise those similarities, means that there is a base immunity in the population against any virus that looks similar to Sar-Cov-2. And many of those similar viri have already been part of our regular seasonal cold selection for years. This is further underlined by the fact that in parts of Asia where the 2002 Sars outbreak was particularly bad, people were less affected by Covid-19, because people exposed to Sars already had antibodies effective against Sars-CoV-2.

And finally, the fact that scientists are working on a vaccine against Covid-19 based on high genetic similarity to Sars-1, should really get everyone to stop the term “novel”. Novel implies it’s more scary and thus stokes unnecessary fear and overreaction by the public, media, and governments. Any serious scientist should have never suggested that this was a novel virus.

Addendum based on a comment I received and sort of a summary of this article: The PCR test is a viral test, to see, if you have a virus in your body. People who are tested between getting infected and some time after having an immune response, will come back positve. I am not sure for how long after an immune response, but possibly weeks after they still have the mentioned viral debris in their body (i.e. left-over bits of the destroyed virus). But over time that viral debris does get removed from the body and then people come back negative. The viral test is not the same as an antibody test. Antibodies are proteins that are built after you had an infection of a specific disease. They remain in your body and that’s what causes immunity to a certain disease. So the antibody tests look for those proteins, not for the virus, they look for immunity, rather than infection.

So in conclusion, if you’ve had a Sars-Cov-2 infection, after some time the PCR viral test should come back negative, but the antibody test should always come back positive.

I am a scientist and writer. I aim to be a voice of reason and facts in this distorted world in which opinions are considered truth.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store