Our family immunizes selectively, probably on a different basis of selection than others. Our daughter is receiving her MMR series, as well as DTaP, and polio, so far, because we've had no contra-indications in the family and feel that these vaccinations have been around longer therefore making more testing and data available, and also that these diseases are more serious dangers not only because of the reaction they might cause but because many docs now practicing will have never seen a case and the delay in accurate diagnosis/treatment. All of that said, just to add what perspective I am bringing to the issue.
Which is this: No, I don't feel that "Patient Zero" should have a responsibility to any others harmed as a result of a disease that is vaccine-preventable. No. 1, even this supposed "Patient Zero" must have had exposure/gotten the disease somewhere, so it's impossible to determine where to pass the buck. No. 2, this "Patient Zero" and/or family has already been "punished" for their choices - they have had the same disease. No. 3, it would be long and costly to implement a system that would allow this to happen, as surely it would have to have exemptions for situations such as if "Patient Zero" was found to be in a category that had unquestionable exemption from immunization, such as a child too young to be immunized or one with serious documented previous reactions who was not given a full schedule, or for people who were under a reasonable assumption that they were properly immunized. And No. 4, once we begin assigning blame for transmitting vaccine-preventable illnesses, where does it end?
Sometimes, bad things just happen and there is no legal "fault."