# Explain how vaccination confers protection against a specific pathogen without the individual being exposed to the active disease.

> IB DP Biology Standard Level (2023 syllabus) — C3.2 Defence against disease · Explain · 4 marks

## Mark scheme (4 marks)

1. The vaccine contains antigens (or weakened/killed pathogens/attenuated pathogen/subunit proteins) that do not cause disease but are recognised as foreign (non-self).
2. The antigens stimulate an adaptive (primary) immune response, leading to clonal selection and expansion of specific B and/or T lymphocytes.
3. Memory cells (B memory cells and/or T memory cells) are produced and persist long-term in the body.
4. Upon later exposure to the real pathogen, memory cells enable a faster and larger secondary immune response, producing antibodies quickly enough to prevent disease.

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