I wonder how often severe COVID disease in healthy young adults is due to undiagnosed IgA deficiency? Elevated IL-8 may be a biomarker for both IgA deficiency and severe disease.

I wonder if this could account for men being 2-3 times more likely to have severe/fatal COVID?

In this study of 7293 healthy Caucasians, 0.21% had IgA deficiency and 2.13% had subnormal IgA. Men were more likely than women to have IgA deficiency or insufficiency, 0.93% vs 2.66%, respectively, which amounts to 2.86 times more likely. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2362.2004.01311.x#ss9-title