The rapid development of multiple vaccines providing strong protection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been a major achievement. There is now compelling evidence for the role of neutralizing antibodies in protective immunity. T cells may play a role in resolution of primary SARS-CoV-2 infection, and there is a widely expressed view that T cell-mediated immunity also plays an important role in vaccine-mediated protection. Here we discuss the role of vaccine-induced T cells in two distinct stages of infection: firstly, in protection from acquisition of symptomatic SARS-CoV-2 infection following exposure; secondly, if infection does occur, the potential for T cells to reduce the risk of developing severe COVID-19. We describe several lines of evidence that argue against a direct impact of vaccine-induced memory T cells in preventing symptomatic SARS-CoV-2 infection. However, the contribution of T cell immunity in reducing the severity of infection, particularly in infection with SARS-CoV-2 variants, remains to be determined. A detailed understanding of the role of T cells in COVID-19 is critical for next-generation vaccine design and development. Here we discuss the challenges in determining a causal relationship between vaccine-induced T cell immunity and protection from COVID-19 and propose an approach to gather the necessary evidence to clarify any role for vaccine-induced T cell memory in protection from severe COVID-19.

多种疫苗的快速开发为严重急性呼吸综合征冠状病毒 2 (SARS-CoV-2) 感染提供了强有力的保护，这是一项重大成就。现在有令人信服的证据证明中和抗体在保护性免疫中的作用。T 细胞可能在解决原发性 SARS-CoV-2 感染中发挥作用，人们广泛认为 T 细胞介导的免疫在疫苗介导的保护中也发挥着重要作用。在这里，我们讨论疫苗诱导的 T 细胞在感染的两个不同阶段中的作用：首先，在暴露后避免出现有症状的 SARS-CoV-2 感染；其次，如果确实发生感染，T 细胞有可能降低患上严重 COVID-19 的风险。我们描述了一些证据，反对疫苗诱导的记忆 T 细胞在预防症状性 SARS-CoV-2 感染方面的直接影响。然而，T 细胞免疫在降低感染严重程度方面的贡献，特别是在 SARS-CoV-2 变体感染方面，仍有待确定。详细了解 T 细胞在 COVID-19 中的作用对于下一代疫苗的设计和开发至关重要。在这里，我们讨论了确定疫苗诱导的 T 细胞免疫和预防 COVID-19 之间因果关系的挑战，并提出了一种收集必要证据的方法，以阐明疫苗诱导的 T 细胞记忆在预防严重的 COVID-19 中的作用。