A vaccine is most effective if it manages to break chains of transmissions. That means you'd want to optimize for likely chains of transmissions, and not only f

A vaccine is most effective if it manages to break chains of transmissions. That means you'd want to optimize for likely chains of transmissions, and not only for giving it to those vulnerably to the virus. So grandma might need to wait, and the grandkids going to school might get it first, then healthy 20/30-somethings working in public facing jobs etc.