The clinical symptoms of coronavirus disease 2019 (COVID-19) include fever, cough, fatigue, breathlessness, sore throat, and other manifestations (Wu and McGoogan, 2020). The symptoms differ among individuals and disease severity is associated with risk factors such as age, cardiovascular disease, and obesity (Bae et al., 2021). COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which belongs to the beta-coronavirus group within the Coronaviridae family. The receptor binding domain (RBD) of viral spike protein recognizes the host receptor angiotensin-converting enzyme 2 (ACE2) and facilitates viral entry (Walls et al., 2020b; Yan et al., 2020). The mutations on the RBD may influence the biological characteristics of viral spike protein, and enhance its affinity to ACE2. Such modifications can promote viral transmission, modify viral cell tropism, and eventually alter viral pathogenesis and disease severity. Moreover, the immunogenic changes in the RBD can aid escape of the immune response elicited by vaccination. Increased viral transmission and immune evasion have led to the emergence of variants of concern (VOC), which are responsible for the ongoing pandemic.

The development of vaccines is one of the most effective strategies to combat infectious disease. Vaccines can induce a virus-specific immune response, which is also called adaptive immunity. Adaptive immunity comprises four main components: circulating antibodies, memory B cells, CD4+ T cells, and CD8+ T cells. Because of extensive SARS-CoV-2 immunological studies in humans, including diverse COVID-19 vaccine trials and SARS-CoV-2 infection studies, there is an abundance of data on the human SARS-CoV-2-specific immune response. Additionally, there is evidence showing that neutralizing antibodies, memory B cells, CD4+ T cells, and CD8+ T cells play essential roles in protective immunity against SARS-CoV-2, including VOC. In this review, we discuss how the SARS-CoV-2 genetic changes, especially with regard to the VOC, modify viral pathogenesis and how the four components of adaptive immunity recognize diverse SARS-CoV-2 variants.