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9700 · 11.2

Antibodies and vaccination — practice questions

Practice and worked examples for 9700 Antibodies and vaccination. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

In a community of 8,000 people, 92% are vaccinated against a disease. The vaccine is 90% effective. Calculate the maximum number of people who could still contract the disease if exposed. [4 marks]

Show solution outline
  1. Vaccinated population: 0.92×8000=73600.92 \times 8000 = 7360 people.
  2. Vaccine failures: 10%10\% of vaccinated may still be susceptible: 0.10×7360=7360.10 \times 7360 = 736 people.
  3. Unvaccinated: 8000−7360=6408000 - 7360 = 640 people (fully susceptible).
  4. Maximum susceptible if all exposed: 736+640=1376736 + 640 = 1376 people.

This illustrates why high vaccination coverage is needed for herd immunity.

Worked example 2

Distinguish between active and passive immunity, giving one natural and one artificial example of each. [6 marks]

Show solution outline

Active immunity — the body produces its own antibodies and memory cells after antigen exposure.

  • Natural: recovery from measles infection.
  • Artificial: MMR vaccination.

Passive immunity — pre-formed antibodies are received; protection is immediate but short-lived with no memory cells.

  • Natural: IgG crossing the placenta to the fetus.
  • Artificial: injection of antiserum containing monoclonal antibodies.
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