When illness in one person is treated or prevented, others to whom that person is connected also benefit.
This leads to a problem. Taking network effects seriously means that we should value socially connected people more. From a policy perspective—if not a moral perspective—the connected should get more healthcare attention.
More from Nicholas Christakis here (PDF). As Christakis notes, a healthcare system that replaces the current one that grants inexplicit privileges to the wealthy with one that favors the networked might be more just, but the notion makes him uncomfortable.
Without even debating the ethics of such a system, I don't think measuring a person's peer effect multiplier is anywhere near precise enough today. I have nightmarish visions of an angry mob of people waving their Klout scores at the ER waiting room attendant.