Pfizer’s and Moderna’s mRNA-based COVID-19 vaccines have caused injury and death on an unprecedented scale. This short article explains from first principles why adverse events must be expected not just after the first injection of such a vaccine but after each booster shot as well. The argument is not limited to SARS-CoV-2 or its spike protein but applies generally to any non-self antigen introduced in the form of mRNA. Accordingly, not only must the COVID mRNA vaccines be stopped, but mRNA vaccines should never be used again, regardless of the infectious agent in question.