Final answer:
The concept where a secondary immune response produces antibodies against the original pathogen's epitopes, even if the pathogen has changed, is called original antigenic sin.
Step-by-step explanation:
The concept being described when subsequent encounters to an initial pathogen trigger a secondary immune response with antibodies directed against epitopes originally present on the infecting pathogen is known as original antigenic sin. This term refers to the immune system's tendency to preferentially utilize immunological memory based on the first exposure to a particular antigen when encountering similar but not identical antigenic variants in the future. Therefore, the antibodies made during a secondary response are directed towards the epitopes recognized during the primary infection, even if the pathogen has evolved slightly since then. This can sometimes impair the immune system's ability to effectively deal with the new strains of the pathogen.