Her son was born in 2009, just as a novel strain of influenza, the H1N1 virus, began spreading across the United States, and she found herself immediately engaged in an anxious discussion about the merits of infant vaccination. “If we imagine the action of a vaccine not just in terms of how it affects a single body but also in terms of how it affects the collective body of a community, it is fair to think of vaccination as a kind of banking of immunity,” she writes.