3.7.11Inquiry Process
Vaccines and Immunity — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 152 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5How Vaccines Work
1
A vaccine introduces antigens from a pathogen, in a weakened, inactivated or partial form, or as instructions to make an antigen.
2
B lymphocytes with matching receptors are activated, divide, and produce plasma cells that secrete antibodies.
3
Some activated lymphocytes become memory cells, which remain in the body for years.
4
On exposure to the real pathogen, memory cells respond more quickly, producing more antibodies in a secondary response.
5
The pathogen is destroyed before it can cause illness, so the person is immune without having had the disease.
Section 2 of 5Active and Passive Immunity
Active immunity
- Active immunity The body makes its own antibodies and memory cells, either after infection or after vaccination, giving long-lasting protection.
Passive immunity
- Passive immunity Antibodies are acquired from another source,
- such as across the placenta or in breast milk,
- giving protection that is rapid but temporary.
Memory cells
- Memory cells Present only in active immunity, they account for the faster and stronger secondary response.
Boosters
- Boosters Repeated doses strengthen memory for pathogens whose antigens change or whose protection fades over time.
| Feature | Active | Passive |
|---|---|---|
| Antibodies made by | Own plasma cells | Another individual |
| Memory cells | Yes | No |
| Onset | Slow | Immediate |
| Duration | Long | Short |
Section 3 of 5Herd Immunity
Herd Immunity
Concept
- Concept If enough of a population is immune, an infected person has too few susceptible contacts for the disease to spread widely.
Protection of others
- Protection of others People who cannot be vaccinated, such as infants or those with weak immunity, are protected indirectly.
Threshold
- Threshold The proportion that must be immune is about 1 − 1/R₀,
- where R₀ is the average number of people one case infects in a fully susceptible population.
Falling coverage
- Falling coverage If vaccination rates fall below the threshold, outbreaks of diseases such as measles can return.
Eradication
- Eradication Smallpox was eradicated because high vaccination coverage cut off its transmission, showing the power of herd immunity.
Section 4 of 5Worked Example
Question
- Measles has an R₀ of about 15.
- Calculate the approximate proportion of the population that must be immune for herd immunity.
- Threshold = 1 − 1/R₀.
- Substitute R₀ = 15: 1 − 1/15 = 1 − 0.0667.
- Threshold = 0.933, that is 93.3%.
Answer About 93% of the population must be immune.
Section 5 of 5Exam Checklist & Tips
3.7.11 – Key Points for the Exam
- Vaccine A preparation of antigens that stimulates an immune response without causing disease.
- Memory cell Long-lived lymphocyte that allows a rapid response to a repeat infection.
- Herd immunity Indirect protection of a population when a large proportion is immune.
- R₀ Average number of new infections caused by one case in a fully susceptible population.
Common Mistakes
- Saying that vaccines contain antibodies; they contain antigens (active immunity).
- Believing herd immunity requires 100% vaccination.
- Confusing passive immunity, which has no memory cells, with active immunity.
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