6.1 Vaccination

A free GCSE Biology lesson for AQA (8461) from OBA School: how vaccines work, primary and secondary immune responses, and herd immunity. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe how white blood cells make antibodies that are specific to an antigen
• Explain how vaccination makes a person immune to a disease
• Compare the primary and secondary immune responses using a graph
• Explain herd immunity and why a high vaccination rate matters
• Evaluate the benefits and risks of vaccination programmes

Key words

• Pathogen: A microorganism that causes infectious disease (bacteria, viruses, fungi, protists).
• Antigen: A protein (or other molecule) on the surface of a pathogen that white blood cells recognise.
• Antibody: A protein made by white blood cells (lymphocytes) that binds to one specific antigen.
• Vaccine: A small amount of a dead or inactive form of a pathogen (or its antigens) given to make a person immune.
• Immunity: Being able to destroy a pathogen quickly before it causes illness.
• Herd immunity: When so many people are immune that a pathogen cannot spread easily, protecting those who are not immune.

Antigens and antibodies

Every pathogen has antigens on its surface. White blood cells called lymphocytes make antibodies with a shape that is complementary to one particular antigen, so each antibody is specific. Antibodies bind to the antigens and clump pathogens together, so other white blood cells (phagocytes) can engulf and destroy them.

The first time you meet a pathogen, it takes days for lymphocytes to make enough of the right antibody. Meanwhile, the pathogen reproduces and you become ill.

How vaccination works

• Step 1: A small amount of a dead or inactive form of the pathogen is injected (or sometimes taken by mouth or nasal spray).
• Step 2: Its antigens stimulate lymphocytes to make the specific antibodies. This is the primary response. The person does not become ill.
• Step 3: Some lymphocytes stay in the blood as memory cells.
• Step 4: If the live pathogen enters later, memory cells make the correct antibodies quickly and in large amounts (the secondary response). The pathogen is destroyed before it can cause illness.

Exam tip: In an exam answer, link these words in order: dead / inactive pathogen → antigens → white blood cells → specific antibodies → memory → rapid response.

Herd immunity

If a large proportion of a population is immune, a pathogen has few people to pass to, so it cannot spread far. This also protects people who cannot be vaccinated, such as newborn babies or people with weak immune systems.

Worked example: vaccination coverage

A town has 24 000 children. 21 360 have had the MMR vaccine. Health experts say about 95% coverage is needed for herd immunity against measles.
Coverage = 21 360 ÷ 24 000 × 100 = 89%.
95% of 24 000 = 22 800, so 22 800 − 21 360 = 1440 more children need vaccinating.

Answer: 89%; 1440 more children

Benefits and risks

• Has controlled many serious diseases (smallpox has been wiped out; polio is now rare); Risks and problems Mild side effects are common, e.g. a sore arm or a slight fever
• Epidemics can be prevented by herd immunity; Risks and problems Very rarely, a serious reaction such as an allergy
• Cheaper than treating large numbers of ill people; Risks and problems Protection may fade – some vaccines need boosters
• Protects people who cannot be vaccinated; Risks and problems Some pathogens mutate (e.g. flu), so a new vaccine is needed often

Common mistakes

• Saying the vaccine contains antibodies. It contains a dead or inactive pathogen / antigens; your body makes the antibodies.
• Saying antibodies stay in the blood for life. It is the memory cells that remain and respond quickly.
• Saying vaccination kills the pathogen in the vaccine. The pathogen is already dead or inactive.
• Saying “the body remembers the disease”. Say that white blood cells recognise the antigen and make the specific antibodies rapidly.

Revision questions

Try these, then check your answers below each one.

Question 1. What does a vaccine contain? (Choose from: A small amount of dead or inactive pathogen, Antibodies from another person, Antibiotics, White blood cells.)

Answer: A small amount of dead or inactive pathogen

Working: A vaccine contains dead or inactive pathogens (or their antigens), which stimulate white blood cells to make antibodies.

Question 2. Which type of white blood cell makes antibodies?

Answer: lymphocyte

Working: Lymphocytes make antibodies.

Question 3. True or false? An antibody against the measles virus will also protect against the mumps virus.

Answer: False

Working: False. Each antibody fits one specific antigen; mumps has different antigens.

Related lessons

• Previous lesson: 5.12 Required Practicals: Communicable Diseases
• Next lesson: 6.2 Antibiotics and Painkillers
• In this chapter: 6.3 Discovering Drugs
• In this chapter: 6.4 Developing Drugs
• In this chapter: 6.5 Making Monoclonal Antibodies

Continue in the full course

This lesson is section 6.1 (AGCBH0601) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.