How do vaccines confer immunity?

• A. By exposing the immune system to antigens, generating memory cells for faster future responses.
• B. By killing pathogens directly
• C. By replacing damaged tissues
• D. By increasing the number of red blood cells

Answer: (A)

Vaccines confer immunity by training the immune system to recognize a pathogen. They introduce harmless antigens from the pathogen, so immune cells respond without causing disease. This exposure activates B cells to make antibodies and creates memory B cells, and it also engages T cells as needed. Once trained, memory cells persist and enable a rapid, stronger response if the real pathogen is encountered later, often preventing illness or reducing its severity. So the core idea is immune memory built from the initial exposure to vaccine antigens.

Vaccines don’t kill pathogens directly, don’t repair damaged tissues, and don’t increase red blood cell numbers, which is why those options aren’t correct.