Vaccine-associated enhanced disease (VAED) is an immune response to a vaccine that is ‘causally linked’ to a higher risk of adverse outcomes upon infection compared to infection without prior vaccination. (A vaccinated person carries higher risk of suffering from adverse events upon infection)
 The only way to assess the safety & efficacy of a vaccine and address the theoretical risk of VAED is in
a. phase 3 efficacy trials with sufficient numbers of endpoints
b. rigorous post-licensure surveillance.
 If VAED is frequent or clinically distinctive, the clinical trial participants would experience natural infection with SARS-CoV-2.