DSE Biology | Disease and Immunity — Teacher Prep Guide

DSE Biology | Disease and Immunity — Teacher Prep Guide | Chains, antibodies and 80% efficacy

2026-11-05

Tutor lesson-prep guides · Secondary Biology

Students can say the word antibody, then freeze when a vaccine efficacy table appears. This lesson puts the transmission chain, the immune response and the epidemiology numbers on one line.

Objectives — Students will be able to: (1) describe the three links of a transmission chain and the four pathogen groups, and compute herd thresholds from R0 (75% at R0 = 4, 91.7% at R0 = 12); (2) separate innate from adaptive immunity and contrast the primary response (about 14 days) with the secondary response (about 5 days); (3) compute vaccine efficacy from attack rates (4% versus 20%, efficacy 80%).

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Pathogen groups	Main structural difference between bacteria and viruses	Viruses have no cell structure and must parasitise
Percentages	What percentage is 8 out of 200	4%
Immune memory	Why a vaccinated person fights the same pathogen faster	Memory cells respond at once

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Transmission chain	Pathogen, route and susceptible host; break any link	Name the three links
8-20 min	R0 and herd immunity	R0 = 4 needs 75%, R0 = 12 needs 91.7%	Compute one threshold
20-32 min	Innate versus adaptive	Skin, phagocytes, inflammation versus B and T cells	Sort ten cards
32-40 min	Primary and secondary	About 14 days versus 5 days, 16 times higher	Sketch both curves
40-45 min	Vaccine efficacy	8/200 versus 40/200, efficacy 80%	Work alone

03 Teaching script (read it out)

Scene 1: The chain and R0: maths decides how many need the jab

A transmission chain has a pathogen, a route and a susceptible host. Masks break the route, vaccines make hosts less susceptible, and breaking any link stops transmission. R0 is the average number of people one case infects.
The herd threshold is 1 – 1/R0: 75.0% (that is 75%) at R0 = 4, and 91.7% at R0 = 12. The more contagious the pathogen, the higher the share with immunity must be.

Ask students: compute the threshold for R0 = 3 themselves (about 66.7%) and explain why it is not 100%.

Scene 2: Innate and adaptive: two lines of defence

Innate immunity is immediate and not antigen specific: skin and mucosa, phagocytes, inflammation. Adaptive immunity targets a specific antigen and takes time to start: antigen presentation, helper T cells, antibody-producing B cells and cytotoxic T cells.
Key numbers: the primary response peaks at about 14 days, the secondary at about 5 days with 16 times the antibody (four doublings). That is what a vaccine does: it trains the response in advance, it does not build a wall.

Ask students: sort ten immune-cell cards into innate and adaptive piles, writing one function per card.

Scene 3: Vaccine efficacy from attack rates

A trial of 400 people: 8 of 200 vaccinated participants fell ill (4%), against 40 of 200 controls (20%). Efficacy is 1 – 0.04/0.20 = 80%.
Note what that means: it is not “80% of people cannot be infected”, it is an 80% reduction in risk for those vaccinated. Without a control group the number means nothing.

Ask students: recompute efficacy if the control group had only half as many cases, and say why the denominator cannot be swapped freely.

04 Question types and worked steps

Type	Example	Steps	Answer
Epidemiology numbers	Attack rate or R0 to threshold and trend	Write the definition, substitute, then add units and one sentence	R0 is an average, not a constant
Ordering the immune response	Sequence from antigen to antibody	Antigen, presentation, helper T, B cell, plasma cell, antibody	Antibodies come from plasma cells
Vaccines and herd immunity	Efficacy or required coverage	Efficacy divides two attack rates; threshold uses 1 – 1/R0	The two formulas are not interchangeable
Experimental design	Design controls and variables	Same pathogen, same age, placebo, double blind	No control, no conclusion

Sanity check (teach this): Sanity checks: the vaccinated attack rate 4% is below the control 20%, so efficacy is positive and sits between 0 and 100; the threshold for R0 = 4 (75%) is below that for R0 = 12 (91.7%), as a more contagious pathogen requires more coverage; the secondary response at 5 days is faster than the primary at 14 and reaches 16 times the titre.

05 Independent practice (3 questions)

Question	Answer	What to watch
Transmission chain	Give the three links for influenza in a school and one way to break each	One measure per link, and say which is easiest
Herd immunity	Threshold for a pathogen with R0 = 5	1 – 1/5, written as a percentage
Immune response	Three differences between primary and secondary responses	Timing, peak and duration
Vaccine efficacy	8 of 200 vaccinated and 40 of 200 controls fell ill, find efficacy	Divide the two attack rates, then subtract from one

06 Common mistakes and what to say

Mistake	Student writes	Say this
Reading efficacy as a protection rate	Saying 80% of people are completely immune	Efficacy is how far risk falls, not how many cannot be infected. Vaccinated people can still be infected, just less often.
Confusing R0 with the threshold	Treating R0 = 4 as 4% coverage needed	R0 is how many one case infects; the threshold is the share needing immunity. Different formulas.
Antibodies from B cells directly	Writing that B cells kill pathogens	B cells become plasma cells to secrete antibodies, and antibodies bind pathogens rather than killing them.
No control group	Comparing illness before and after a campaign	Without controls you cannot separate the vaccine from seasonality, so the conclusion will not stand.

07 Homework (paper, section and question numbers)

Secondary Biology chapter index — Every chapter in the subject
All teacher prep guides — Guides for other subjects
Redo this chapter — Recompute both efficacy figures and sketch the two response curves

08 Exit check (last 5 minutes)

Question	Answer	Decision
Herd immunity threshold formula	1 – 1/R0	Answering R0 itself means repeat act two
Which response is faster	Secondary, about 5 days against 14	Answering that they are equal means repeat act two
How efficacy is calculated	One minus vaccinated attack rate over control attack rate	Answering with deaths means repeat act three

09 Tutor FAQ

What does 80% efficacy mean?

A vaccinated person carries about one fifth of the risk of an unvaccinated one, an 80% reduction, not a guarantee against infection.

Does R0 change?

Yes. Contact rates, density and interventions all move it, so use the figure the question provides.

Why booster doses?

Antibody levels and memory cells wane, and pathogens with high R0 need a larger immune share to stop transmission.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.