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How A UT Southwestern Lab Is Examining COVID-19 Variants In North Texas

Sign that says rapid COVID testing here daily.
Keren Carrión

As COVID case numbers continue to rise in North Texas, new strains have emerged, like the mu variant. But the delta variant continues to cause the majority of infections in the region.

Dr. James Cutrell is an associate professor in the Department of Internal Medicine at UT Southwestern Medical Center. He talked with Think host Krys Boyd about how doctors in UT Southwestern labs are examining cases from across the region, and what they're learning about the different COVID variants.


How COVID-19 Mutates Into Variant Strains

The SARS COVID virus, which is what causes COVID-19, is an RNA virus. So, in the process as it's copying its genetic material or its RNA to make copies of new viruses, it periodically will make mistakes or errors.

Many of those errors lead to dead ends, the virus just stops replicating. But occasionally it will lead to a mutation or a change that actually provides a selective advantage for that particular variant of the virus, maybe it's more easily transmitted, maybe it's able to escape prior immunity.

When there are millions and millions of hundreds of millions of cases, as what we've seen, over time the virus gets enough opportunities that some of those selected mutations can develop into these variants that we've seen.

Mutations In Immunocompromised People

We do think that at least some of these variants may have arisen in individuals who have a suppressed immune system. Because of that, the virus is able to replicate or grow for a longer period of time in that individual's body, because they're not ever able to control the virus.

We do think some of these variants could have arisen from individuals who had suppressed immune systems. But other variants likely just arose from the natural course of infecting so many people.

How Strains Are Detected

A key part of this is what we call surveillance. So there are public health labs, as well as university labs, really all across the country and all across the world that take positive samples, and then do genetic sequencing to detect either existing or known variants or to detect changes that could be an indication of a new variant.

Then those are compared against really a library of sequences of known variants to track the percentage and the growth of particular variants in a geographic region.

My colleagues at UT Southwestern have been doing this type of sequencing on all of our positive cases, dating back to January 2021. So we've been able to have a picture as to how these specific variants are spreading here in North Texas.

Why The Delta Variant Is The Dominant Variant In North Texas Right Now

What we have seen is the variants that have spread the most widely are really the ones that have that transmission advantage.

If you look back in the winter, we had the alpha variant, which was originally described in the UK. It was about 50% more transmissible than the original virus. That was really what drove the wave that we saw on this country and really around the world back in December and January.

The delta variant is even more highly transmissible than that. The suggestion is that it's 100% more transmissible or twice as easily spread as the original virus. It's really that ability of the virus to be more easily spread and transmitted that has allowed delta to become the dominant variant here in the U.S., here in North Texas, as well as globally.

This interview has been lightly edited for clarity.

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Got a tip? Email Galilee Abdullah at

Galilee Abdullah is an arts reporter.