We are part of a group of clinicians, scientists, and patient advocates who have lodged a formal “Citizen Petition” with the United States Food and Drug Administration (FDA), asking the agency to delay any consideration of a “full approval” of a covid-19 vaccine. The message of our petition is “slow down and get the science right—there is no legitimate reason to hurry to grant a license to a coronavirus vaccine.” We believe the existing evidence base—both pre- and post-authorization—is simply not mature enough at this point to adequately judge whether clinical benefits outweigh the risks in all populations. The covid-19 vaccines in widespread use have emergency authorizations (EUA), not actual approvals, a crucial regulatory distinction that reflects major differences in the level of regulatory scrutiny and certainty about the risk-benefit balance. Our petition doesn’t argue that risks outweigh benefits—or that benefits outweigh risks. Rather, we focus on methods and processes, outlining the many remaining unknowns about safety and effectiveness—and suggest the kinds of studies needed to address the open questions.