世界卫生组织25日发布的每日疫情报告说，迄今尚无证据表明拥有新冠抗体的康复者可免于“二次感染”。
世卫组织指出，通过自然感染对病原体产生免疫是一个多步骤过程，通常需要1至2周。感染病毒时，人体首先出现非特异性的固有免疫应答，巨噬细胞、嗜中性粒细胞和树突状细胞可减慢病毒感染进程，甚至阻止症状出现。在此之后，人体出现适应性免疫应答，产生与病毒特异性结合的抗体，即免疫球蛋白；还会产生T细胞，识别和清除受感染细胞，即细胞免疫。
世卫组织说，如果适应性免疫应答足够强，则可以阻止病情发展为重症，或防止同一病毒的“二次感染”。迄今大多数研究表明，新冠康复者体内拥有新冠病毒抗体，但其中一些人血液中的抗体水平非常低。由此推断，细胞免疫可能对病人的康复也至关重要。
世卫组织强调，截至4月24日,尚无研究对新冠病毒抗体是否赋予人类对该病毒的免疫力进行评估。此外，对人体内新冠病毒抗体的实验室检测需要进一步验证，以确定检测的准确性和可靠性。
针对一些国家政府建议将抗体检测作为发放“免疫护照”或“无风险证书”的基础，从而允许持证人能够出行或恢复工作，世卫组织认为，没有足够证据证明抗体介导免疫的有效性，进而无法保证此类证书的准确性。
世卫组织警告，那些检测显示拥有抗体的人们也许自认为可免于“二次感染”，进而忽略公共卫生建议。因此，使用此类证书可能增加病毒继续传播的风险。
There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection, the World Health Organization (WHO) said in a daily situation report on Saturday.
Although many studies show that people who recovered from COVID-19 have antibodies to the novel coronavirus, also known as SARS-CoV-2, the WHO noted, some of these people have very low levels of neutralizing antibodies in their blood.
"As of April 24, 2020, no study has evaluated whether the presence of antibodies to SARS-CoV-2 confers immunity to subsequent infection by this virus in humans," stressed the UN health agency.
Some countries have suggested that the detection of antibodies to the novel coronavirus could serve as the basis for an "immunity passport" or "risk-free certificate", which would enable individuals to travel or return to work, assuming that they are protected against re-infection.
However, there is still a lack of sufficient evidence for the effectiveness of antibody-mediated immunity to guarantee the accuracy of an "immunity passport" or "risk-free certificate, the WHO underlined, warning that "the use of such certificates may therefore increase the risks of continued transmission."
According to the UN agency, laboratory tests that detect antibodies to SARS-CoV-2 in people, including rapid immunodiagnostic tests, need further validation to determine their accuracy and reliability.
