Serology and COVID-19

By: Kylie Luo


As of January 30, 2020, the novel coronavirus was declared a global health emergency. Many countries across the globe reacted in similar ways, implementing a stay-at-home or quarantine order. With the high transmissibility of the virus and the lack of treatment, many companies are rushing to develop a vaccine to help aid the cause of COVID-19. But in order to properly administer a treatment or vaccine, proper and efficient diagnosis must first be developed.


Since the beginning of the outbreak, diagnosis of the virus has been a primary concern. Testing for the virus began as a molecular test where a swab would be placed in a patient’s nose in order to obtain a sample of cells from the upper respiratory tract, where the virus first manifests. This sample would then be transferred to a lab to be tested and compared to the DNA of the virus. The issue with molecular testing, however, is that it takes 24 to 48 hours to be able to see results. In addition to the high transmissibility of COVID-19, the number of people who are developing symptoms of the virus is constantly increasing, making the time constraint of molecular tests inefficient.


In order to resolve the time constraint of molecular testing, companies have been attempting to develop new methods of more efficient testing. These come in the form of serological tests, which test blood samples for the presence of COVID-19. When a foreign invader, or antigen, enters the body, the immune response produces specific antibodies in order to fight the antigens. Serological tests are made to test for the antibodies produced in response to the antigens. Though over 70 tests have been developed in this form, none of them are FDA approved. This is mainly because serological tests detect the concentration of a target in a sample. If the concentration is too low, the target is undetectable, leading to many false negative results.


A common form of serological testing for the coronavirus, called the enzyme-linked immunosorbent assay (ELISA) test, involves the use of a detection enzyme, that when bonded to the proper target and mixed with a substrate, will produce a measurable color that indicates the concentration of a target in a sample. The three main forms of testing are shown in the diagram above. Direct ELISA indicates that only a primary antibody is being used to catch the target. Once the target binds to the antibody, the enzyme is activated, releasing a color. Similarly, indirect ELISA activates the enzyme conjugate through binding, but through the use of a secondary antibody. In an indirect ELISA, the primary antibody catches the secondary antibody that has the enzyme conjugate, which then can catch the target and release the color. Lastly, in sandwich ELISA, a primary antibody without the enzyme conjugate is added to a plate, which catches the target. The target is then added to a secondary antibody with the enzyme conjugate also binded to the target, creating a sandwich.


This form of testing can take as little as 15 minutes, which would greatly increase the rate of diagnosis. Moreover, serological testing can determine if a patient has recovered from COVID-19. After the body recovers, the antibodies for the invader still remain in case the body encounters the same invader again. This is important for data and research collection, and even has the potential to provide information regarding better and faster development of a treatment to this pandemic.


Overall, the possibility of serological testing has opened many new doors, not only in the field of diagnosis, but also under the topic of finding a cure. Since it is faster and possibly more efficient than the widely used molecular tests, it has much greater potential to help flatten the curve of COVID-19.




Citations:

http://www.epitopediagnostics.com/covid-19-elisa

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2366430/

https://www.cdc.gov/coronavirus/2019-ncov/lab/serology-testing.html

https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-serological-test-validation-and-education-efforts


What Did You Learn?


Questions:


1. What is the difference between molecular and serological testing in terms of COVID-19?


Molecular testing uses a swab to collect a sample from the upper respiratory tract which is then used to compare to the virus to diagnose a patient. These tests tend to take time as it requires isolation of certain particles. Similarly, serological tests use a blood sample to test for the concentration of the virus. Unlike molecular tests, these provide almost immediate results, as an indicator is used and is triggered if the concentration of the virus is high enough.



2. Why does the amount of time a diagnosis test take matter?


With constant cases on the rise, more and more people are getting tested, but between the time of testing and results, a suspected carrier could interact with more people, given a longer period of diagnosis time, contributing to the spread of the virus. Essentially, faster diagnosis rates can lead to more efficient isolation of the virus, helping it to draw to a close sooner than later.


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