11.2.610-11 · Infectious Disease and Immunity

Vaccination to Control Disease — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 9 parts Lesson 20 of 21 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision

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Lesson summary

11.2.6 Vaccination to Control Disease — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain herd immunity, describe vaccination programmes and evaluate their success and problems.Meaning — when a high proportion of a population is immune, the pathogen has few susc…

Protected groups
Childhood diseases
Falling coverage
Routine childhood programmes
Ring vaccination
Mass campaigns

Part 1 of 7Herd immunity

Herd immunity

Meaning

Meaning when a high proportion of a population is immune, the pathogen has few susceptible hosts and the chain of transmission is broken.

Protected groups

Protected groups even unvaccinated individuals such as babies, those allergic to the vaccine and the immunocompromised.

Childhood diseases

Childhood diseases vaccines against mumps, chickenpox and whooping cough, given on an immunisation schedule, keep them at low levels.

Threshold

Threshold it is approximately 1 − 1/R₀, where R₀ measures how infectious a disease is.
Measles has R₀ between 12 and 18, so about 92 to 95 per cent must be immune.
A disease with R₀ of 2 needs only about 50 per cent.

Falling coverage

Falling coverage outbreaks occur if coverage falls below the threshold, as in measles when parents avoid MMR because of unfounded fears.

Part 2 of 7Types of vaccination programme

Types of vaccination programme

Routine childhood programmes

Routine childhood programmes vaccines on a schedule, with boosters, for diphtheria, tetanus, whooping cough, polio, measles, mumps and rubella.

Ring vaccination

Ring vaccination vaccinating everyone near a case to contain an outbreak, as in smallpox eradication.

Mass campaigns

Mass campaigns for example polio immunisation days, which have reduced polio to a few countries.

Targeted programmes

Targeted programmes annual influenza vaccines for the elderly and health workers, and travel vaccines.

Part 3 of 7Conditions favouring success

Conditions favouring success

Vaccine

Vaccine it should be safe, effective, cheap and easy to store.

Pathogen

Pathogen it should have stable antigens and no animal reservoir.

Health system

Health system good infrastructure and trained staff.

Society

Society public trust and education, and high coverage across the population and the world.

Part 4 of 7Successes and difficulties

Disease	Outcome
Smallpox	Eradicated in 1980
Polio	Eliminated from most regions; a few cases persist where there is conflict or poor access
Measles	Large reductions, but outbreaks if coverage drops
HPV	Vaccine reduces cervical cancer risk

Difficulties

Difficulties refusal because of misinformation, cost of vaccines and storage, political unrest and poor access.

Antigenic variation of pathogens.

The need for repeated boosters.

Rare side effects.

Vaccine-derived viruses (live attenuated polio) that mutate and regain virulence.

Animal reservoirs

Animal reservoirs eradication is much harder where a pathogen also infects animals.

Part 5 of 7Evaluation

Individual

Individual protection against a possibly serious illness at a very small risk of side effects.

Community

Community fewer cases, lower healthcare costs and protection of the vulnerable.

Costs

Costs the vaccine, administration and monitoring of side effects.

Data questions

Data questions compare incidence before and after, or calculate the percentage needing vaccination for herd immunity.

Antibiotic link

Antibiotic link fewer infections mean fewer antibiotic prescriptions.

Part 6 of 7Ethical and social issues

Free riding

Free riding a person who does not vaccinate benefits from others' herd immunity while adding some risk to the community.
Some countries make certain vaccines compulsory for school entry.
Others rely on education and incentives.

Arguments

Arguments supporters of compulsion say the public benefit outweighs individual choice;
- opponents stress personal freedom and the right to refuse treatment.

Animals

Animals some vaccines are tested on animals or made using animal cells.

Fair access

Fair access wealthy countries may obtain new vaccines first while poorer regions have less supply.

Risk communication

Risk communication a very small side-effect risk must be set against the much larger risk of the disease.
Public confidence can fall quickly after a false claim and take years to rebuild.

Discussion method

Discussion method give at least one point for each side, use biology such as herd immunity thresholds, and reach a reasoned conclusion.

Part 7 of 7More from the specification

1Active immunization against bacterial toxins

Active immunization against bacterial toxins vaccination with detoxified antigenic toxins induces long-lived immunological memory against lethal microbial infections.

2Passive immunity

Short-term immunity from antibodies given by another individual.

3Receptor protein

Protein on the postsynaptic membrane that binds neurotransmitter.

4Plasma

The liquid part of blood.

5Specific

Able to act on only one type of substrate.

6Hybridoma

A fused plasma cell and tumour cell that makes one antibody.

7Tumour

A lump of cells formed by uncontrolled division.

8Toxin

A poison released by bacteria.

9Monoclonal antibody

Identical antibodies from one clone, all binding the same epitope.

10Plasma cell

A differentiated B cell that secretes antibodies.

11Active immunity

Immunity from making your own antibodies and memory cells.

12Secondary response

Secondary response memory cells make a later infection trigger faster and greater antibody production,
- so the pathogen is cleared before symptoms appear.

Key terms

Term	Meaning
Herd immunity	Protection of a population when enough people are immune.
Ring vaccination	Vaccinating contacts of cases to contain an outbreak.
R_{0}	The average number of people infected by one case in a susceptible population.
Immunisation schedule	A planned timetable of vaccines given to children.
Eradication	Permanent removal of a disease worldwide.
Coverage	The proportion of a population that has been vaccinated.

Avoid these mistakes

Saying herd immunity needs 100 per cent coverage — the threshold depends on R_{0}.

Saying herd immunity protects only vaccinated people — it also protects the unvaccinated.

Saying all pathogens can be eradicated like smallpox — animal reservoirs and variable antigens prevent it.

Saying vaccines have no risks — side effects are rare but real.

Last updated: 18 October 2026