The preponderance of ChAdOx1-S/ChAdOx1 nCoV-19-associated cases should result in consideration of a role also for the vector (rather than the SARS-CoV-2 spike protein used as immunogen) and of adjuvants in future studies investigating the aetiopathogenesis of MOG-EM after SARS-CoV-2 vaccination. This evidence concerns the gene MOG and erythema multiforme.