The coronavirus disease 2019 (COVID-19) pandemic that caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected millions of people and is an ongoing issue globally. The application of effective and safe vaccines is critical to achieving control of the pandemic.¹ Data from clinical trials have shown that several vaccines can induce humoral and cellular immune responses against SARS-CoV-2.^2,3,4 However, given the long time required for vaccine production, difficulty in vaccine distribution and public skepticism about their safety and benefits, the vaccine coverage rate is growing slowly worldwide. Therefore, to make full use of available resources and maximize the efficacy of vaccination is critically important in fighting against COVID-19.