It can happen in both normal antibodies or a vaccine (or gene therapy) when the bond strength between the antibody and pathogen is very weak. A slight mutation in the pathogen can cause an enhanced viral effect where the antibody actually makes the pathogen worse than if it were not there.
What happens is as follows:
Against origin pathogen, the antibody weakly binds to pathogen neutralizing it and is able to stay that way.
Pathogen mutates slightly.
Against mutated pathogen, the antibody weakly binds to pathogen.
The bound pair enters in the cell (the cell lets it in as it recognizes the antibody).
The antibody breaks away from the pathogen due to the weak bond being even weaker than original due to the mutation.
The antibody effectively acted as a taxi service for the pathogen into the cell and the method of infecting the cells.
ADE = Antibody Dependent Enhancement
It can happen in both normal antibodies or a vaccine (or gene therapy) when the bond strength between the antibody and pathogen is very weak. A slight mutation in the pathogen can cause an enhanced viral effect where the antibody actually makes the pathogen worse than if it were not there.
What happens is as follows:
The antibody effectively acted as a taxi service for the pathogen into the cell and the method of infecting the cells.