Original antigenic sin

Antibodies or T-cells induced during infections with the first variant of the pathogen are subject to repertoire freeze, a form of original antigenic sin.

According to Francis as cited by Richard Krause:[7] The antibody of childhood is largely a response to dominant antigen of the virus causing the first type A influenza infection of the lifetime.

Between primary and secondary infections or following vaccination, a virus may undergo antigenic drift, in which the viral surface proteins (the epitopes) change through natural mutation.

[11] However, the impact of antigenic sin on protection has not been well established and appears to differ with each infectious agent vaccine, geographic location, and age.

[9] The relative ineffectiveness of the bivalent booster against the SARS-CoV-2 Omicron variant in patients who had previously received COVID-19 vaccines has been attributed to immunological imprinting.

[13] It has been demonstrated that during a second infection by a different strain of dengue virus, the CTLs prefer to release cytokines instead of causing cell lysis.

The original antigenic sin: When the body first encounters an infection it produces effective antibodies against its dominant antigens and thus eliminates the infection. But when it encounters the same infection, at a later evolved stage, with a new dominant antigen , with the original antigen now being recessive, the immune system will still produce the former antibodies against this old "now recessive antigen" and not develop new antibodies against the new dominant one. This results in the production of ineffective antibodies and thus a weak immunity.
A memory B cell specific for Virus A is preferentially activated by a new strain, Virus A 1 , and produces antibodies that ineffectively bind to the A 1 strain. These antibodies inhibit activation of a naive B cell that produces better antibodies against Virus A 1 . This effect leads to a diminished immune response against Virus A 1 and heightens the potential for serious infection.