“For example, rhesus macaques who were vaccinated with the Spike protein of the SARS-CoV virus demonstrated severe acute lung injury when challenged with SARS-CoV, while monkeys who were not vaccinated did not.
Similarly, mice who were immunized with one of four different SARS-CoV vaccines showed histopathological changes in the lungs with eosinophil infiltration after being challenged with SARS-CoV virus. This did not occur in the controls that had not been vaccinated.
A similar problem occurred in the development of a vaccine for FIPV, which is a feline coronavirus.”
“A major trigger for ADE is viral mutation. Changes to the amino acid sequence of the Spike Protein (which is the protein on the virus that facilitates entry into our cells via the ACE2 receptor) can cause antigenic drift.
What this means is that an antibody that was once neutralizing can become a non-neutralizing antibody because the antigen has slightly changed.
Therefore, mutations in the Spike protein that naturally occur with coronaviruses could presumably result in ADE. Since these future strains are not predictable, it is impossible to predict if ADE will become a problem at a future date.”