Vaccine hesitancy in America didn't begin with the uproar over the mRNA vaccines for Covid-19. The late twentieth and early twenty-first centuries saw resistance to a wide variety of vaccines. In Unvaccinated Under God, Kira Ganga Kieffer shows that debates over vaccine safety and mandatory vaccination were about more than diseases or injections. Kieffer argues that vaccine hesitancy in the U.S. should be understood as religious expression—not as the product of scientific misinformation. Through a series of historical case studies, which range from the "mother warriors" who claimed a link between the MMR vaccine and autism during the 1990s to opposition to masking and vaccines during the Covid-19 pandemic, Kieffer frames vaccination controversies as contests over religious freedom and moral authority. These debates concerned bodily, spiritual, and sexual purity; the morality of state-mandated medical risk; the importance of children; and the authority of parents and doctors. With this new, illuminating perspective on vaccine hesitancy, Kieffer offers a novel and even-handed way to understand Americans' changing and increasingly divided attitudes toward biomedical knowledge and technology. Her account offers listeners an accessible set of tools for how to "think with religion" when it comes to contemporary contests over medical authority.