The 'Doctrine of Original Antigenic Sin', first phrased by Francis, Davenport & Hennessy in 1953, and followed up by occasional papers in the 1960s and 1970s, has lived a life in obscurity and negligence ever since it was postulated. From time to time, and with long intervals, papers on the subject appear. And almost invariably, they are quickly forgotten. Although many will erroneously use the phrase 'Antigenic Sin' to describe classical cross-reactions, the term should be reserved to describe the strain-specific serological response to earlier influenza strains after infection or vaccination with later variants, irrespective of whether one or more antigenic shifts had occurred during the observation period of the study. It is unlikely that antibodies generated under the mechanism of Antigenic Sin will have any major epidemiological relevance.