For millennia, humans have sought and found purpose, solace, values, understanding, and fellowship in religious practices. Buddhist nuns performed variolation against smallpox over 1000 years ago. Since Jenner developed vaccination against smallpox in 1796, some people have objected to and declined vaccination, citing various religious reasons. This paper reviews the scriptural, canonical basis for such interpretations, as well as passages that support immunization. Populous faith traditions are considered, including Hinduism, Buddhism, Jainism, Judaism, Christianity, and Islam. Subjects of concern such as blood components, pharmaceutical excipients of porcine or bovine origin, rubella strain RA 27/3, and cell-culture media with remote fetal origins are evaluated against the religious concerns identified. The review identified more than 60 reports or evaluations of vaccine-preventable infectious-disease outbreaks that occurred within religious communities or that spread from them to broader communities. In multiple cases, ostensibly religious reasons to decline immunization actually reflected concerns about vaccine safety or personal beliefs among a social network of people organized around a faith community, rather than theologically based objections per se. Themes favoring vaccine acceptance included transformation of vaccine excipients from their starting material, extensive dilution of components of concern, the medicinal purpose of immunization (in contrast to diet), and lack of alternatives. Other important features included imperatives to preserve health and duty to community (e.g., parent to child, among neighbors). Concern that 'the body is a temple not to be defiled' is contrasted with other teaching and quality-control requirements in manufacturing vaccines and immune globulins. Health professionals who counsel hesitant patients or parents can ask about the basis for concern and how the individual applies religious understanding to decision-making about medical products, explain facts about content and processes, and suggest further dialog with informed religious leaders. Key considerations for observant believers for each populous religion are described.