Instead of comparing COVID-19 to controls, what about comparing severe COVID-19 to mild COVID-19? You could find genes that are linked to worse side effects. This could help doctors with assigning treatments. The dataset we used in this course has data for severe and mild COVID-19, if you remember.
Find your own dataset! Gene Expression Omnibus has thousands of public gene expression datasets. You can find your own on virtually any disease you want, from Alzheimer's to pancreatic cancer to diabetes.
Check out these papers I wrote for examples/inspiration. (bottom of page)
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