Which change exemplifies antigenic variation in SARS-CoV-2?

• A. Mutation of spike proteins
• B. Mutation in the nucleocapsid protein
• C. Changes in replication rate
• D. Alterations in capsid structure

Answer: (A)

Antigenic variation means changes in the parts of the virus that the immune system recognizes, especially the surface antigens targeted by antibodies. For SARS-CoV-2, the spike protein is the main surface antigen and the primary target of neutralizing antibodies and vaccines. When spike mutates, the antibody binding sites (epitopes) can be altered, reducing how well antibodies recognize the virus and enabling partial immune escape. This makes mutations in spike proteins the clearest example of antigenic variation. Mutations in the nucleocapsid protein, changes in replication rate, or alterations in capsid structure don’t alter the key antigenic sites that antibodies most commonly target, so they’re less representative of antigenic variation in this context.