Dr. Ezekiel Emanuel is ready to step out and party - well, almost. The chair of the department of medical ethics and health policy at the University of Pennsylvania hasn't been to the theater in over a year and he says he's "dying to go." He's also planning to travel to Switzerland this summer. But first, he has to sort out a big open question - both for himself, and for anyone he's going to share some air with. "How am I supposed to prove that I've been vaccinated?" he asks. "What I have now is a CDC cardboard piece...