CHAPTER 3: Understanding the Emergence of SARS-CoV-2 Viral Variants From a Genomic Perspective

Clinical manifestations of coronavirus disease 2019 (COVID-19) include asymptomatic to mild and severe disease which is predominantly associated with respiratory distress. COVID-19 poses a grave challenge to global health systems. Until November 2020, the whole world was focused on tackling what was thought to be a single coronavirus variant. However, more evolving variants have changed the scenario, leading to the terms such as variants of concern and variants of investigation (D614G, 20I/501Y.V1,20H/501Y.V2, CAL.20C etc.). In this chapter, we have encapsulated classification, structure and evolution of genetic variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and provided information about vaccines and their response to multiple viral variants. A spike protein is the key target for most antibodies against the virus, which are generated either during infection or after vaccination. The structural substitutions found in the variant of concern have occurred mainly in antibody binding sites, e.g. E484, E417, N501, N439 and N440, which form part of the binding sites of the receptor binding domain (RBD) of the spike protein. This poses difficulties for antibodies to recognize the RBD and to interact with viral spike proteins for their eventual neutralization. Acquisition of antibody resilience and the polyclonal nature of antibodies also play an imperative role in combating viral infection. Emergence of new variants that can evade immunity due to prior vaccination is becoming a major challenge for vaccine developers as they pursue moving targets.