Extended study in people who are out there in a risk situation.

If you vaccinate someone and they make an antibody response, and then they get exposed and infected, does the response that you induced actually enhance the infection and make it worse?

This would not be the first time, if it happened, that a vaccine that looked good in initial safety actually made people worse. There was a history of the respiratory syncytial virus vaccine in children which, paradoxically, made the children worse. One of the HIV vaccines that we tested several years ago actually made individuals more likely to get infected.