For many patients, COVID-19 infections can last a few days, but a growing number of case reports suggest that chronic infections of COVID-19 can last several weeks or even several months. Can this lead to new variants?
While COVID-19 infections have become far less deadly than they were during its first year, this elusive virus’ ability to evolve and mutate has led to the development of various variants, begging the question—where do these variants come from, and what circumstances allow them to exist?
A new study titled “Drivers of adaptive evolution during chronic SARS CoV-2 infections” from Tel Aviv University and Sourasky Medical Center aimed to answer this question. The study, led by Professor Adi Stern and doctoral student Sheri Harari of the Shmunis School of Biomedicine and Cancer Research at TAU’s Wise Faculty of Life Sciences, in collaboration with Dr. Yael Paran and Dr. Suzy Meijer of Sourasky Medical Center, explored where variants of the COVID-19 virus come from. The study was published in Nature Medicine.
Exploring drivers of adaptive evolution for chronic COVID-19
For many patients, COVID-19 infections can last a few days, but a growing number of case reports suggest that chronic infections of COVID-19 can last several weeks or even several months. These growing cases led researchers to hypothesize that variants of concern derived from these chronic infections.
In this study, researchers sought out drivers of emerging variants of concern by consolidating sequencing results from a set of 27 chronic infected patients at Sourasky’s Ichilov Hospital in Tel Aviv. Due to either hematologic cancer, direct anti-B cell treatment, high dosage steroid treatment, or very low CD4+T cell counts, they inferred that all 27 patients were immunocompromised. Researchers then tested the ability to associate antibody evasion mutations with patient-specific and virus-specific features correlated with the emergence of variants.
Impacts from infected immunocompromised patients
The results of this study found the following:
- In immunosuppressed patients, weakened antibody responses can prevent full recovery and cause the virus to mutate many times during a lengthy infection
- The ability of the virus to survive and reproduce in immunocompromised without restriction has led to the development of many variants of the virus
- Variants found among chronically ill COVID-19 patients may have the same mutations in their evolution as those in variance they have the potential to cause severe illness
These findings suggest that while rapidly spreading variants are less common among strains originating from immunosuppressed patients, they are more likely to emerge when global infection rates rise.
Upon closer examination of these patients, researchers found that in patients who have been chronically ill with COVID-19, the virus continues to thrive in the lungs of the patient. Based on the data, researchers believe that the virus accumulates mutations within the lungs and then travels back to the upper respiratory tract.
The complexity of the COVID-19 virus it's still something researchers are trying to understand, but this study highlights the importance of protecting immunocompromised patients, especially chronically ill COVID-19 patients, as they may be harboring the next variant that could threaten patients around the world.