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mystlurker t1_jdk8n7n wrote on March 25, 2023 at 12:11 AM

Reply to comment by im_thatoneguy in What happened to the old COVID variants, like Delta? Could they come back? by number1dork

This article is pretty interesting:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3734171/

I found potential explanation #4 to be of particular interest. There is a theory that exposure to another flu strain in ~1890 may have caused a dysregulated immune response.