Immune Memory Fails on Mutated Antigens

Steps:

• Vaccination creates memory B and T cells specific to the original influenza antigen.
• Viral mutation alters the antigen, making it unrecognizable to these memory cells (statement 3).
• Without recognition, no rapid secondary immune response occurs (statement 2).
• The mutated antigen acts as novel, triggering a slower primary immune response (statement 1 false).

Why D is correct:

• Immunological memory requires antigen specificity; mutations change epitopes, blocking secondary response recall as defined in adaptive immunity.

Why the others are wrong:

• A: Includes 1, but primary response occurs to new antigens.
• B: Includes 1 (false) and omits 3 (memory non-recognition).
• C: Includes 1, which incorrectly denies primary response capability.

Final answer: D