Covid-19 vaccines are a critical tool for controlling the pandemic. While safe and effective vaccines have been developed, research is expected to continue for many years regarding the optimal implementation of existing vaccines in specific settings, and the development of second-generation vaccines that may offer advantages in terms of either efficacy or ease of implementation. Given this context, some commentators have argued that new Covid vaccine trials should be able to use placebo controls, and that existing studies should be able to continue with blinded participants in order to collect high quality, unbiased data. Using international ethics guidance documents, this paper argues against placebo controls, given the existence of proven effective interventions, and against protracted blinding once safety and efficacy milestones have been met. Instead, it advocates for study designs that allow for direct comparison between approved and experimental vaccines, which facilitates both data collection and greater access to vaccines.