Immunity is a multifaceted phenomenon. For T cell-mediated memory responses to SARS-CoV-2, it is relevant to consider their impact both on COVID-19 disease severity and on viral spread in a population. Here, we reflect on the immunological and epidemiological aspects and implications of pre-existing cross-reactive immune memory to SARS-CoV-2, which largely originates from previous exposure to circulating common cold coronaviruses. We propose four immunological scenarios for the impact of cross-reactive CD4⁺ memory T cells on COVID-19 severity and viral transmission. For each scenario, we discuss its implications for the dynamics of herd immunity and on projections of the global impact of SARS-CoV-2 on the human population, and assess its plausibility. In sum, we argue that key potential impacts of cross-reactive T cell memory are already incorporated into epidemiological models based on data of transmission dynamics, particularly with regard to their implications for herd immunity. The implications of immunological processes on other aspects of SARS-CoV-2 epidemiology are worthy of future study.

免疫是一个多方面的现象。对于 T 细胞介导的针对 SARS-CoV-2 的记忆反应，需要考虑它们对 COVID-19 疾病严重程度和病毒在人群中传播的影响。在这里，我们反思了免疫学和流行病学方面以及预先存在的 SARS-CoV-2 交叉反应免疫记忆的影响，这主要源于之前接触过流行的普通感冒冠状病毒。我们针对交叉反应 CD4 ⁺记忆 T 细胞对 COVID-19 严重程度和病毒传播的影响提出了四种免疫学方案。对于每种情况，我们讨论了其对群体免疫动态的影响以及 SARS-CoV-2 对人类的全球影响的预测，并评估其合理性。总之，我们认为交叉反应性 T 细胞记忆的关键潜在影响已经被纳入基于传播动力学数据的流行病学模型中，特别是它们对群体免疫的影响。免疫过程对 SARS-CoV-2 流行病学其他方面的影响值得未来研究。