在当前仍无特效药可用的前提下，疫苗的接种作为最可行且可及的新冠肺炎（COVID-19）疫情控制手段在全球开展。病毒感染后诱导机体产生的特异性免疫保护反应对于病毒的清除至关重要，这也是疫苗策略的理论基础。然而，针对新冠病毒（SARS-CoV-2）的获得性免疫持续性以及免疫保护效应这两个关键科学问题还未被解答。本团队前期一系列队列研究，证实了新冠肺炎康复者SARS-CoV-2特异性体液免疫水平在急性期达到峰值后逐渐降低的变化以及免疫记忆的存在。本课题借助国内疫情发生较早的前提，率先对自然感染康复者进行为期三年的体液免疫水平动态随访，并对低抗体滴度的部分个体通过灭活疫苗接种的方式激发SARS-CoV-2免疫记忆，并利用假病毒对免疫效应的交叉保护性进行评估。本项目的开展将为该病毒的深入了解、疫苗接种策略的制定、应对下一步疫情变化、疫情防控工作提供具有重要意义的参考。

With the ongoing emergence of the novel coronavirus (SARS-CoV-2) variants，it is too early to expect that the pandemic would be end soon. In the context of lacking of specific medicine, vaccination has been accepted as one of the most feasible and accessible means of coronavirus disease (COVID-19) control strategies around the world. The specific protective immunity induced by viral infection plays a key role in the elimination of virus and is also the theoretical basis of vaccination strategy. Two key scientific questions about duration of adaptive immunity and immunoprotection remain unknown. Our team had described the changes of humoral response which increases to the peak in the early acute phase and decreases gradually in a serial of cohort studies. Moreover, the presence of immunological memory had been observed. In this study, based on the fact of earlier outbreak of COVID-19 in China, we would be the first to do the follow-up visit for three years. Part of COVID-19 convalescents who have neutralizing antibody with low titers will be chosen for vaccination to induce immunological memory. Then, cross protection produced by immunological memory for SARS-CoV-2-S variants will be assessed. This study will reveal the immune persistence and cross protection and contribute to the comprehensive understand of this virus, formulation of vaccination strategies and the reference of further change of pandemic.