(CNN) - Despite all his medical knowledge, 31-year-old medical student and PhD candidate Sean Doyle couldn't know for certain all the risks of the injection he had just received in his right shoulder at Emory University Hospital. Yes, of course he was told of the potential side effects, such as soreness in his arm, a fever, malaise. But when you are among the first people in the world to receive a vaccine injection, the real answer about the risks is simply "we don't know."