A person receives a vaccination against influenza. Some months later, the same person is exposed to the influenza virus. Explain why the person does not develop the disease on this second exposure.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Vaccination programmes are used worldwide to protect individuals from communicable diseases. The influenza vaccine introduces antigens into the body without causing the disease itself.
Model answer (5 marks)
The influenza vaccine contains viral antigens that are recognised by the immune system. B‑lymphocytes are activated and produce antibodies that are specific to these antigens. The primary response also generates memory B‑cells. When the person is later exposed to the influenza virus, the memory cells recognise the same antigens and mount a secondary response. This response is faster and stronger, producing large amounts of antibody quickly enough to neutralise the virus before symptoms appear, so the person does not develop the disease.
Examiner tips
- Use the term ‘memory cells’ and explain they recognise the same antigen
- Show that the secondary response is faster and produces more antibody
- Mention that the antibodies neutralise the pathogen before symptoms develop
Common mistakes
- Confusing the vaccine with the disease itself
- Failing to mention memory cells or the speed of the secondary response
- Using vague phrases like ‘immune system’ without specifying B‑cells or antibodies
Mark scheme (5 marks)
- The vaccine contains antigens from the influenza virus
- B-lymphocytes are activated and produce antibodies specific to those antigens
- Memory cells are produced following the first immune response (to the vaccine)
- On second exposure, memory cells recognise the same antigen and respond faster / more quickly than the primary response
- Large quantities of antibodies are produced quickly enough to destroy the pathogen before symptoms develop / before the person becomes ill
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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