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B6.1 Vaccination

GCSE Combined Science · AQA · Chapter B6: Preventing and Treating Disease

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: how vaccines work, primary and secondary immune responses, boosters 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 lymphocytes 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

  • Antigen: A protein (or other molecule) on the surface of a pathogen that white blood cells recognise.
  • Antibody: A protein made by lymphocytes that binds to one specific antigen.
  • Antitoxin: A protein made by lymphocytes that neutralises a toxin made by a pathogen.
  • Vaccine: A small amount of a dead or inactive form of a pathogen, with 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, antibodies and memory

Every pathogen has antigens on its surface. White blood cells called lymphocytes make antibodies whose shape is complementary to one particular antigen, so each antibody is specific. Antibodies bind to the antigens and clump pathogens together so that phagocytes can engulf them. Lymphocytes can also make antitoxins, which neutralise toxins.

The first time you meet a pathogen, it takes several days for lymphocytes to make enough of the right antibody. Meanwhile the pathogen reproduces and you become ill. Afterwards, memory cells stay in the blood.

How vaccination works

  • Step 1: A small amount of a dead or inactive form of the pathogen is injected (some vaccines are swallowed or sprayed into the nose). It has the same antigens as the live pathogen.
  • Step 2: The antigens stimulate lymphocytes to make the specific antibodies: the primary response. The person may feel slightly unwell for a day or two, but does not get the disease.
  • Step 3: Memory cells remain in the body.
  • Step 4: If the live pathogen enters later, memory cells make the right antibodies quickly and in large amounts (the secondary response), so the pathogen is destroyed before it can make the person ill.

For some vaccines a booster dose is given months or years later. It produces a secondary response and tops up the number of memory cells. The MMR vaccine, for example, protects against measles, mumps and rubella and is given as two doses in early childhood.

Exam tip: In an exam answer, link these words in order: dead / inactive pathogen → antigens → lymphocytes → specific antibodies → memory cells → rapid secondary 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 young babies or people with weak immune systems. If vaccination rates fall, the disease can spread quickly again.

Worked example: vaccination coverage

A city has 32 000 children aged 5. 29 120 have had both doses of MMR. About 95% coverage is needed for herd immunity against measles.
Coverage = 29 120 ÷ 32 000 × 100 = 91%.
95% of 32 000 = 30 400, so 30 400 − 29 120 = 1280 more children need vaccinating.

Answer: 91%; 1280 more children

Benefits and risks

  • Has controlled many serious diseases (smallpox has been wiped out; polio is now very 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 change their antigens (e.g. flu), so a new vaccine is needed often

Common mistakes

  • Saying the vaccine contains antibodies. It contains a dead or inactive pathogen with its antigens; your body makes the antibodies.
  • Saying antibodies stay in the blood for life. It is the memory cells that remain and respond quickly.
  • Mixing up antigen (on the pathogen) and antibody (made by your lymphocytes).
  • Saying “the body remembers the disease”. Say that memory 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 a dead or inactive form of the pathogen, Antibodies against the pathogen, Antibiotics, White blood cells.)

Answer: A small amount of a dead or inactive form of the pathogen

Working: A vaccine contains a dead or inactive pathogen with the same antigens as the live one. Lymphocytes respond by making antibodies.

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

Answer: lymphocyte

Working: Lymphocytes make antibodies (and antitoxins). Phagocytes engulf pathogens.

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

Answer: False

Working: False. Each antibody fits only one antigen; the rubella virus has different antigens.

Related lessons

Continue in the full course

This lesson is section B6.1 (AGCSC0601) of our free GCSE Combined Science 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 Combined Science course.

 

 

 

 

 

 

 

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