When primary immunity is boosted not by the homologous but by a crossreacting vaccine,
the newly formed antibodies react better with the primary antigen than with the antigen
actually eliciting the response. This phenomenon bears the name of Original Antigenic Sin
(1). It is shown that the number of antibody molecules produced against the original and the
vaccinating antigen is the same; that each of these molecules is capable of reacting with
both antigens; that the activity of an antiserum can be completely absorbed with either …

It is difficult to explain the phenomenon of original antigenic sin [this Bulletin, 1954, v. 29, 16]
that human beings respond to influenza vaccines by producing antibodies against the first
influenza virus they experienced as children in higher titre than antibodies against the virus
in the vaccine-by the two chief theories of antibody production. I. To try to explain this
phenomenon, sera taken from children in influenza vaccine trials in 1954 were re-examined
by equilibrium filtration [ibid., 1962, v. 37, 902]. The children, whose first experience of …