Explain how vaccination protects individuals from disease by stimulating the immune system.

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

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A vaccine contains antigens (or weakened/killed pathogens or attenuated pathogen components) that do not cause disease. These antigens trigger an immune response, activating lymphocytes – B cells and/or T cells – and leading to the production of specific antibodies. During this primary response, memory B cells and memory T cells are generated and persist in the body. When the individual is later exposed to the same pathogen, these memory cells recognise the antigen rapidly, producing a faster and stronger secondary immune response, which prevents or greatly reduces the severity of disease.

Examiner tips

Use the word ‘antigens’ and mention weakened/killed/attenuated forms; link to ‘no disease’. Show the sequence: antigen → lymphocyte activation → antibody production → memory cell formation. Explain that memory cells give a quicker, stronger response on re‑exposure. Use correct terminology: B cells, T cells, antibodies, memory cells, primary/secondary response.

Common mistakes

Confusing vaccine with disease-causing pathogen; forgetting that the vaccine does not cause disease. Omitting the role of memory cells or the secondary response. Using vague terms like ‘immune system’ without specifying lymphocytes, antibodies or memory cells.

Mark scheme (4 marks)

A vaccine contains antigens (or weakened/killed pathogens or attenuated pathogen components) that do not cause disease
The antigens trigger an immune response, including activation of lymphocytes (B cells and/or T cells) and production of antibodies
Memory cells (B memory cells and/or T memory cells) are produced and persist in the body after the initial immune response
Upon subsequent exposure to the same pathogen, memory cells enable a faster and stronger secondary immune response, preventing or reducing the severity of disease

Key terms in this question

vaccination