Protective immune memory—through B cells, which make antibodies, and/or T cells, which in the case of CD8+ T cells can kill virus-infected cells—can be induced by identical but also by related viruses. Related to the COVID-19 virus SARS-CoV-2, there are four common cold coronaviruses (CCCoVs) that together cause ~20% of common cold infections: OC43, HKU1, 229E, and NL63. Most adults have been infected with CCCoVs multiple times in their lives. Whether or not meaningful CCCoV-induced anti-SARS-CoV-2 neutralizing antibodies exist remains a matter of debate. Meanwhile, the generation of T cell memory should depend on the genetic make-up of the infected individual. Namely, immune recognition by T cells depends on the presentation of peptides (“epitopes”) by polymorphic major histocompatibility complex (MHC) molecules, and different MHC alleles (variants between individuals) present different peptides from the same pathogen.