https://sciencewithdrdoug.com/2020/08/01/is-a-coronavirus-vaccine-a-ticking-time-bomb/
“Explanation how ADE works and the future perils it may bring.
For a vaccine to work, our immune system needs to be stimulated to produce a neutralizing antibody, as opposed to a non-neutralizing antibody. A neutralizing antibody is one that can recognize and bind to some region (‘epitope’) of the virus, and that subsequently results in the virus either not entering or replicating in your cells.
A non-neutralizing antibody is one that can bind to the virus, but for some reason, the antibody fails to neutralize the infectivity of the virus. This can occur, for example, if the antibody doesn’t bind tightly enough to the virus, or the percentage of the surface area of the virus covered by the antibody is too low, or the concentration of the antibody is not high enough. Basically, there is some type of generic binding of the antibody to the virus, but it fails to neutralize the virus.
In some viruses, if a person harbors a non-neutralizing antibody to the virus, a subsequent infection by the virus can cause that person to elicit a more severe reaction to the virus due to the presence of the non-neutralizing antibody. This is not true for all viruses, only particular ones. This is called Antibody Dependent Enhancement (ADE), and is a common problem with Dengue Virus, Ebola Virus, HIV, RSV, and the family of coronaviruses. In fact, this problem of ADE is a major reason why many previous vaccine trials for other coronaviruses failed.