# Explain how a vaccine protects a person from becoming seriously ill if they are later exposed to a pathogen.

> Eduqas A-Level Biology — 3.3 Microbiology · Explain · 5 marks

> Vaccines contain weakened or inactive forms of a pathogen, or antigens from a pathogen. They are given to individuals to provide protection against communicable diseases.

## Mark scheme (5 marks)

1. The vaccine introduces antigens into the body / the immune system detects the antigens from the vaccine
2. Lymphocytes produce antibodies that are specific / complementary to the antigen
3. Memory cells are formed after the initial immune response
4. When the same pathogen enters the body again, memory cells recognise the antigen and respond more quickly / rapidly produce large quantities of antibodies
5. The pathogen is destroyed before it can cause serious illness / symptoms do not develop because the pathogen is neutralised rapidly

## Related

- [Revision notes for Eduqas A-Level Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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