The mRNA vaccines that have been used against COVID-19 have caused injury and death on an unprecedented scale in the history of medicine. This book documents some of these harms. However, its main purpose is more general: it argues that these harms had to be expected from first principles of immunology, and furthermore that they result from the inherent properties of the mRNA technology as such, rather than from the specific properties of the COVID vaccines. We must therefore expect that future mRNA vaccines against other infectious agents will be similarly toxic.