On March 11^th, 2020, the World Health Organization declared COVID-19 infection as a pandemic. Since it is a novel virus, there are basically no proven drugs or therapies; although many laboratories in different countries are working to develop a vaccine, it will take time to make it available. Passive immunization is the therapy born from the intuition of Behring and Kisato in the late 19^th century. It was widely used for the treatment of bacterial infections until the discovery of antibiotics, as well as during the viral pandemics of the 20^th century and of the beginning of the 21^st; it still has clinical applications (e.g., tetanus prevention). This paper summarizes the basic principles of passive immunization, with particular reference to convalescent plasma. The literature concerning its use during past epidemics and the results of the first clinical studies concerning its use during the current pandemic are discussed too. A large section is dedicated to the analysis of the possible, although rare, side effects. Recently, in 2017, the WHO Blood Regulators Network (BRN) published a position paper, recommending convalescent plasma as the first-choice treatment to be tested in the absence of authorized drugs; however, this strategy has not been followed. In the current epidemic, the principle of passive immunization through convalescent plasma has been applied in several circumstances and particularly in patients with serious complications. The first reported results are encouraging and confirm the effectiveness of plasma therapy and its safety. Also, the FDA has proposed plasma treatment in order to face the increasingly complex situation and manage patients with serious or immediately life-threatening COVID-19 disease. Several studies and clinical programs are still ongoing.

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恢复期血浆：治疗 COVID-19 患者的具有挑战性的工具——过去的教训和新的视角

2020 年3 月 11 日^，世界卫生组织宣布 COVID-19 感染为大流行病。由于它是一种新型病毒，基本上没有经过验证的药物或疗法；尽管不同国家的许多实验室正在努力开发疫苗，但将其投入使用还需要时间。^{被动免疫是19世纪末}贝林和基萨托凭直觉诞生的疗法。^{在抗生素发现之前，以及在 20世纪和 21世纪}初的病毒大流行期间，它被广泛用于治疗细菌感染；它仍然具有临床应用（例如破伤风预防）。本文总结了被动免疫的基本原理，特别是恢复期血浆。还讨论了有关其在过去流行病期间使用的文献以及有关其在当前大流行期间使用的首次临床研究的结果。很大一部分致力于分析可能出现的（尽管很少见）副作用。最近，2017年，世界卫生组织血液监管网络（BRN）发表了一份立场文件，建议在没有授权药物的情况下将恢复期血浆作为首选治疗方法进行测试；然而，这一策略并未得到遵循。在当前的疫情中，通过恢复期血浆被动免疫的原理已应用于多种情况，特别是对于患有严重并发症的患者。首次报道的结果令人鼓舞，证实了血浆疗法的有效性及其安全性。此外，FDA 还提议进行血浆治疗，以应对日益复杂的情况并管理患有严重或立即危及生命的 COVID-19 疾病的患者。多项研究和临床项目仍在进行中。