ABSTRACT
COVID-19 has become a global pandemic, and an effective vaccine is needed. During the outbreak, the urgency for developing candidate vaccines has brought distinct challenges to clinical development. An efficacy trial, which measures whether the vaccine reduces the incidence of disease, is ordinarily required to fully evaluate vaccine efficacy. However, emergency use may be possible if promising immunogenicity results are observed. A ring vaccination trial, which recruits subjects connected to a known case either socially or geographically, is a solution to evaluate vaccine efficacy and control the spread of the disease simultaneously although its conduct is challenging. Nevertheless, when COVID-19 becomes a recurrent epidemic, an 'individual-level' efficacy trial is preferred. Innovative statistical designs, including seamless design, platform trial, master protocol design, are helpful to accelerate clinical development. A seamless Phase I/II design has been applied in multiple COVID-19 vaccine studies to date. However, Phase II/III design should be done very carefully. The control of type I error, maintaining trial blinding and statistical methods leading to unbiased estimates should be pre-specified in the clinical protocol. A Data Safety Monitoring Board is especially important, given the need to assure an adequate level of safety when society want a safe and effective vaccine.