Explain active immunity after infection or vaccination
Use a supplied response model to compare first and later matching exposures.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall active immunity and complementary antigen recognition.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Who produces antibodies in active immunity?
What you will learn
- Two routes stimulate the host
- Read the response model cautiously
| Day | First exposure | Later matching exposure |
|---|---|---|
| Day 0 | 0 | 0 |
| Day 2 | 0 | 5 |
| Day 4 | 2 | 12 |
| Day 6 | 5 | 11 |
| Day 8 | 4 | 9 |
| Day 10 | 3 | 7 |
WHO background: how vaccines work. The plotted values and practice records are invented teaching examples.
Two routes stimulate the host
Active immunity can develop after infection by a pathogen or after vaccination. Both can expose the immune system to relevant antigens and stimulate antibody production within the host. The routes differ in how that exposure occurs: infection involves the pathogen, while vaccination presents appropriate antigen material in a controlled way.
This biological description is not a recommendation to seek infection. Infection can cause disease and its outcome is not established by an immunity diagram. Vaccination is designed to stimulate protection without requiring the person to experience the corresponding natural disease; not every vaccine contains a live weakened pathogen.
Read the response model cautiously
The plotted values are invented teaching data, not clinical measurements: days 0, 2, 4, 6, 8 and 10 after exposure. First-exposure antibody levels are 0, 0, 2, 5, 4 and 3 arbitrary units; later matching-exposure levels are 0, 5, 12, 11, 9 and 7. In this model the later response rises sooner and peaks higher.
The mechanism is immune memory from an earlier active response. Compare the labelled days and values rather than treating the curve as a universal human timetable or protection threshold. A response to a different non-matching antigen cannot automatically be predicted from this graph. Memory-cell production is made explicit in the next vaccination lesson.
Pause and explain
What does this later matching-exposure curve show?
Worked example
In the supplied model, compare the day and size of the highest values for first and later exposure.
Show the worked solution
- First reaches 5 at day 6.
- Later reaches 12 at day 4.
Answer First peak: day 6, 5 units. Later peak: day 4, 12 units.
Try a topic test
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name the two routes to active immunity required here.
Give me a hint
Both stimulate the host response.
Compare my reasoning
- One follows infection.
- The other follows vaccination.
After infection by a pathogen or after vaccination.
Look for these in your work
- Name both routes
- Keep host production
Using the plotted data, calculate the rise from day 2 to day 4 for the later response.
Give me a hint
Subtract the earlier value from the later one.
Compare my reasoning
- Day 2 is 5 units; day 4 is 12 units.
- 12 − 5 = 7.
A rise of 7 arbitrary units.
Look for these in your work
- Use the correct series
- State the model units
Can the graph establish that every vaccinated person becomes protected by day 4 against every disease?
Give me a hint
Consider model status and specificity.
Compare my reasoning
- The data are invented and give no protection threshold.
- Only a matching antigen response is modelled.
No; it is a teaching model of a matching response, not a universal timetable or evidence of protection against all diseases.
Look for these in your work
- State the model limit
- Retain antigen specificity
Common mistakes
- Treating invented units as clinical protection thresholds.
- Assuming infection is a harmless route to protection.
What can you explain now?
What does this later matching-exposure curve show?
Compare with the explanation
Earlier and higher response in the supplied model
Read only the stated data.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Read both peaks without looking, then explain one limitation of the plotted model.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.