Vaccination stimulates adaptive immunity Steps:

• Vaccination introduces antigens from pathogens to trigger immune response without causing disease.
• This activates B and T cells, producing memory cells for long-term protection.
• Effects include antibody production, cellular immunity, and prevention of infection spread.
• All listed effects (1: antigen recognition; 2: memory cell formation; 3: herd immunity contribution) align with immunological principles.

Why A is correct:

• A includes all three effects, matching vaccination's role in humoral and cellular immunity per immunology definitions.

Why the others are wrong:

• B omits 3, but vaccinations contribute to herd immunity by reducing transmission.
• C omits 2, but memory cells are essential for lasting protection.
• D omits 1, but antigen introduction is the primary mechanism.

Final answer: A