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Frank Bures: Rapid antigen COVID tests and omicron variant

From the COLLECTION: Recent Healthful Hints columns by Dr. Bures series
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The SARS-CoV-2 virus is still teaching us. It keeps mutating, twisting and turning to stay alive by infecting us in different forms and variants. The variant now occupying people’s minds, bodies and thoughts is the omicron one. It seems to be overall more able to be transmitted between people but perhaps does not create as vicious a level of disease and death, especially in those vaccinated.

From the beginning, obtaining tests to find out who is infected has been a major effort. In just the last several months, brands of at-home varieties called rapid antigen tests (RATs) have proliferated like rabbits (or rats?). With the holidays still going on, people have been buying them to do their own testing before convening to laugh, celebrate and still not spray viruses hither and yon.

The question is whether the tests can detect the new mutation, omicron. The short answer is yes, but with some qualifications. The COVID-19 virus is made up of its genetic material, its RNA or ribonucleic acid (not DNA). It is covered and protected by a protein coating dubbed a nucleocapsid (NEW-klee-o-CAP-sid) or capsule for the RNA. And the coronaviruses have the additional feature of their infamous “spike proteins” on that protein surface to enable it to attach to (unwilling) host human cells and facilitate their invasion.

Omicron’s unique multiple mutations are mostly in that spike protein, but it only has 4 in the nucleocapsid proteins, two more than delta strain. (Stay with me through the next slog. Refresh your coffee.) The RATs attempt to find the viral capsule proteins and not the spike protein. Most experts are thinking (betting) the RATs will bind to those preferentially. A Dec. 20 MedPage Today article noted that while there are no rigorous, independent studies on RAT, Amy Karger, MD, PhD, clinical pathologist at the University of Minnesota, said she “doesn’t see anything to indicate that we’re going to have trouble detecting omicron with these at-home tests.”

RATs are also called lateral flow tests because the sample from your snoot is put into a tiny well onto special paper inside the test kit prepared with antibodies to the capsule proteins, which are the antigens in RATs. The lab-made antibodies in the paper are like the ones your body would have made against the virus naturally. As the liquid flows along the paper, laterally and literally, any viral antigens will bind to the antibodies and show up as a line to produce a positive result. No line, no antigens, no virus. Yahoo. Well …

There are several small issues in doing the test, among them timing and technique of taking the sample, and quantity of antigen proteins to extract. As of this writing omicron’s time from infection to symptoms is roughly 2-3 days, delta’s 4-5, and the earlier variants 5-7. The most viruses are present when symptoms start. The caveat with omicron is it replicates more efficiently in windpipe/bronchus than nose or upper throat. If people balk at doing the nose swabbing well and long enough, the sample swab won’t soak up as many viruses.

The at-home and even hospital tests don’t use those 4-foot-long (seems like) swabs to go clear back to your throat (and do a brain biopsy at the same time). Hardly anyone would delight in self-sampling with one of those masochistic tools. The other issue with self-done RATs is sample timing. There is some difference of opinion among “experts” whether to test closer or farther from presumed exposure because omicron multiplies (and divides?) faster. However, the United Kingdom’s Health Security Agency tested five of its lateral flow brands of RATs and found no false negative results.

The other type of testing looks for the viral nucleic acids or RNA. These are called RT-PCR or PCR tests, or nucleic acid amplification tests, NAATs. These are the gold standard. It takes a few days to produce a result. But we’ll save the details for another day, okay?

No test or vaccine or mask is perfect, but they are pretty good at attempting to protect us from getting really sick and dying. We’re in this together, whether we want to be or not. Tests are a tool to help us try not to infect each other. If you use a home RAT, for once feel good about getting testy(ed). You won’t need to get testy later because you didn’t get tested. Hope you can pass the test at the end of this Hint. Class dismissed.

Dr. Bures, a semi-retired dermatologist, since 1978 has worked Winona, La Crosse, Viroqua and Red Wing. He also plays clarinet in the Winona Municipal Band and a couple dixieland groups. And he does enjoy a good pun.


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