Vaccination is intended to generate immunity, via immunological memory and circulating specific antibodies, before a person encounters a specific, virulent pathogen for the first time.

(a) During a primary immune response, a process occurs that results in changes to the antigen-binding site of the antibody encoded by an activated B cell. What is the name given to this process?

1. Affinity maturation
2. Class switching
3. Clonal expansion
4. Somatic hypermutation

During a primary immune response, changes to the antigen-binding site of the antibody encoded by an activated B cell occur through a process called somatic hypermutation. This is part of the affinity maturation mechanism that enhances the immune system's ability to respond to pathogens upon subsequent exposures. Therefore, the correct option is 4. Somatic hypermutation.

Explanation:

The process that occurs during a primary immune response resulting in changes to the antigen-binding site of the antibody encoded by an activated B cell is known as somatic hypermutation. During this process, the B cell's antibody genes undergo a high rate of mutation, leading to the generation of antibodies with increased affinity for the specific antigen encountered.

This forms part of the overall mechanism of affinity maturation, a key aspect of the adaptive immune response which ensures that on subsequent exposures to the same pathogen, the immune system can react more effectively. Immunization via vaccination exploits this principle by introducing a harmless version of the pathogen to stimulate memory cell production and prime the immune system for future encounters with the real pathogen without causing the disease.