COVID testing - The Basics

As Colorado and the rest of the country slowly reopen after the COVID pandemic, there is much talk about testing. Some say testing is not helpful or practical while others claim that the entire population needs to be tested before we have even a prayer of life returning to semi-normal. Both are incorrect and hopefully, this will serve as a short primer on COVID testing.

There are two types of tests, an antigen test and an antibody test. Both have their place, but neither is a magic bullet.

Antigen testing is based on PCR technology able to detect minute amounts of viral antigen, which covers the sur face of the virus, from nasal swabs or saliva. This test will tell you if you have virus in your body at the time of the test.

But it won’t tell you if you were infected a month ago or if you are susceptible to infection next week. It’s only a snapshot in time. Think of police radar noting your speed at a given moment without regard to how fast you were driving before or after the recording.

If one is sick with virus symptoms, it is reasonable to be tested although treatment is based on symptoms, not simply a positive test. Regardless of test results, one would still be considered contagious and should self-quarantine or be hospitalized, whether their symptoms are due to COVID or influenza.

Antibodies are formed after the previous infection and COVID antibody tests will tell you if you had been infected in the past. They cannot determine if you are currently infectious as it takes several weeks for antibodies to the virus to develop after infection. Presumably, antibodies mean that you are protected from future infection from COVID, but not necessarily.

These tests are useful to track COVID in the population so we can know what percent of people have been infected, and how many infected are asymptomatic versus extremely ill. It also allows an accurate calculation of the death rate. We know how many people have died from the virus, although that number itself may be wildly inaccurate, the true death rate depends on how many were infected.

Problems remain as the tests are new and their accuracy may be suboptimal. An antibody test telling someone they have immunity when they don’t can be dangerous to them and others.

Antigen testing for the entire US population of 325 million is impossible. And it would only answer who had a virus in their body at the time of testing, not who recovered from the previous infection or who has yet to be exposed. And several days later such testing would have to be repeated as people either get exposed or recover from the virus, changing the test results.

Testing the entire population three times a week is a billion tests per week and impractical. If such testing is necessary to reopen the economy, then just turn out the lights and say game over.

Questions also remain about antibody testing. How soon after infection does one develop antibodies? How long will antibodies protect one from reinfection? Immunity from one strain of the cold virus isn’t protective against the next one yet the previous infection with measles or mumps confers lifetime immunity. What will COVID immunity look like?

Such testing is important but will evolve over time in terms of accuracy and utility. Waiting for the perfect test however, is a fool’s errand as one doesn’t and may never exist. Reopening the economy must rely on more than simply testing.