# A person receives a vaccine against measles. Some years later, the same person is exposed to the measles virus. Explain why the person does not develop the disease.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 6 Immunity, Infection and Forensics · Explain · 5 marks

> Vaccines contain antigens that stimulate the immune system without causing disease. Memory cells produced after vaccination can persist in the body for many years.

## Mark scheme (5 marks)

1. The vaccine introduces antigens (from the measles virus) into the body
2. White blood cells (lymphocytes) produce antibodies specific to the measles antigen
3. Memory cells are produced after the initial vaccination
4. On re-exposure to the measles virus, memory cells recognise the antigen and respond rapidly
5. Antibodies are produced in large quantities quickly enough to destroy the virus before symptoms develop / disease occurs

## Key terms

- [vaccine](https://www.gradenine.co.uk/glossary/vaccine)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-person-receives-a-vaccine-against-458e4093) · Published by Druglandscape Ltd.