Sign in to read the full-text of this chapter for free. Don’t have an account? Register now.

Coronavirus disease-19 (COVID-19) is extremely contagious and involves infection by the virus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). Clinical manifestations of COVID-19 include asymptomatic to mild and severe disease which is predominantly associated with respiratory distress. COVID-19 is posing a grave challenge to the global health systems. Until Nov-2020, the whole world was focused on tackling what was thought to be a single coronavirus variant. However, more and more evolving variants (many of them virulent) have changed the scenario, leading to the terms such as variants of concern and variants of investigations (D614G, 20I/501Y.V1,20H/501Y.V2, CAL.20C etc.). In the present article, we have encapsulated classification, structure and evolution of genetic variants of SARS-CoV-2 and also provided information about vaccines and their response to multiple viral variants. Spike protein is the key target for most antibodies against the virus which are generated either during infection or after vaccination. The structural substitution 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 RBD (receptor binding domain of Spike protein). This poses difficulties for antibodies to recognize RBD and to interact with viral spike proteins for its 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 which can evade the immunity due to prior vaccination is becoming a major challenge for vaccine developers as they pursue moving targets.