Immunisation and Antibiotics

What you'll learn

This revision guide covers the key principles of immunisation and antibiotics that you need for WJEC GCSE Biology. You'll understand how vaccines work to provide immunity, why antibiotics are effective against bacterial infections but not viral ones, and the growing problem of antibiotic resistance. These topics are frequently examined and require clear understanding of biological mechanisms and real-world applications.

Key terms and definitions

Vaccination (immunisation) — the introduction of small quantities of dead or inactive pathogens into the body to stimulate white blood cells to produce antibodies, providing immunity without causing disease

Antibodies — proteins produced by white blood cells (lymphocytes) that bind to specific antigens on pathogens, marking them for destruction

Antigen — a protein marker on the surface of a pathogen that triggers an immune response and antibody production

Antibiotics — medicines that kill or inhibit the growth of bacteria inside the body without damaging human cells

Antibiotic resistance — when bacteria evolve so that antibiotics are no longer effective at killing them or stopping their growth

Herd immunity — when a high percentage of a population is vaccinated, reducing disease spread and protecting unvaccinated individuals

Memory cells — specialised white blood cells that remain in the blood after an infection or vaccination, enabling rapid antibody production if the same pathogen re-enters the body

Pathogens — microorganisms that cause infectious disease, including bacteria, viruses, fungi and protists

Core concepts

How vaccination works

When a vaccine is administered, it contains dead or inactive forms of a specific pathogen. These weakened pathogens cannot cause the disease but still carry the characteristic antigens on their surface.

The immune response follows these steps:

1. White blood cells (lymphocytes) detect the antigens on the vaccine pathogens as foreign
2. Specific lymphocytes produce antibodies that are complementary to these antigens
3. The antibodies bind to the antigens, causing the pathogens to clump together
4. Other white blood cells destroy the clumped pathogens by engulfing them (phagocytosis)
5. Some lymphocytes become memory cells that remain in the blood for many years

If the vaccinated person later encounters the live pathogen, their memory cells rapidly produce large quantities of the correct antibodies. This secondary immune response is faster and more effective than the primary response, often destroying the pathogen before symptoms develop. The person is therefore immune to that disease.

Common vaccines in the UK include:

• MMR (measles, mumps and rubella)
• DTP (diphtheria, tetanus and pertussis)
• HPV vaccine
• Annual flu vaccine
• COVID-19 vaccines

Herd immunity and vaccination programmes

Herd immunity occurs when a sufficiently high proportion of a population is vaccinated against a disease. This breaks the chain of transmission because:

• Vaccinated individuals cannot catch or spread the disease
• The pathogen has fewer opportunities to infect new hosts
• Vulnerable people who cannot be vaccinated (babies, immunocompromised individuals) are protected indirectly

For highly contagious diseases like measles, approximately 95% vaccination coverage is needed to achieve herd immunity. For less contagious diseases, lower percentages may suffice.

Vaccination programmes aim to:

• Reduce disease incidence in the population
• Protect vulnerable groups through herd immunity
• Eradicate diseases entirely (as happened with smallpox)
• Prevent epidemics and reduce healthcare costs

When vaccination rates fall below the herd immunity threshold, outbreaks can occur even in populations where most people are vaccinated.

Why antibiotics only work against bacteria

Antibiotics are drugs that target bacterial cells specifically. They work by:

• Damaging bacterial cell walls, causing the cells to burst
• Interfering with bacterial protein synthesis
• Disrupting bacterial DNA replication
• Inhibiting bacterial enzyme activity

Crucially, antibiotics exploit differences between bacterial cells and human cells. For example:

• Bacteria have cell walls; human cells do not
• Bacterial ribosomes differ structurally from human ribosomes
• Bacterial metabolic pathways differ from those in human cells

This selectivity means antibiotics can kill bacteria without significantly harming human cells.

Antibiotics cannot treat viral infections because:

• Viruses lack cell walls and metabolic machinery
• Viruses reproduce inside host cells using host cell mechanisms
• Damaging viral replication would necessarily damage human cells
• Viruses are non-living when outside host cells, so metabolic inhibitors are ineffective

Common misconceptions include expecting antibiotics for colds, flu, or COVID-19. These are viral infections requiring antiviral drugs (if available) or supportive treatment only.

Examples of bacterial infections treatable with antibiotics:

• Bacterial pneumonia
• Tuberculosis (TB)
• Bacterial meningitis
• Strep throat
• Urinary tract infections (UTIs)
• Infected wounds

The development and spread of antibiotic resistance

Antibiotic resistance is one of the greatest threats to global health. The process occurs through natural selection:

1. Mutation — random genetic mutations in bacterial DNA occasionally produce antibiotic-resistant bacteria
2. Selection pressure — when antibiotics are present, non-resistant bacteria die but resistant bacteria survive
3. Reproduction — resistant bacteria reproduce rapidly (binary fission every 20 minutes in optimal conditions)
4. Inheritance — resistant genes pass to offspring, creating a resistant population
5. Spread — resistant bacteria can transfer resistance genes to other bacteria through plasmid exchange

Key examples include:

• MRSA (methicillin-resistant Staphylococcus aureus) — resistant to many common antibiotics, causes difficult-to-treat wound infections
• Drug-resistant tuberculosis — requires lengthy treatment with multiple antibiotics
• Resistant E. coli — causes untreatable urinary and blood infections

Factors accelerating antibiotic resistance:

• Overuse in medicine — prescribing antibiotics for viral infections or minor bacterial infections
• Patients not completing courses — stopping treatment early allows partially resistant bacteria to survive and multiply
• Agricultural use — routine antibiotic use in livestock creates resistant bacteria that can transfer to humans
• Global travel — resistant strains spread rapidly between countries

Reducing antibiotic resistance

Healthcare systems and individuals can slow the development of resistance through:

Medical practice:

• Only prescribe antibiotics for bacterial infections
• Use narrow-spectrum antibiotics targeting specific bacteria when possible
• Reserve broad-spectrum antibiotics for serious infections
• Implement strict hospital hygiene protocols to prevent spread of resistant bacteria
• Develop new antibiotics through research programmes

Individual responsibility:

• Complete the full antibiotic course even if symptoms improve
• Never share antibiotics or use leftover antibiotics
• Do not demand antibiotics for viral infections like colds or flu
• Practice good hygiene to prevent infections requiring antibiotic treatment
• Get vaccinated to reduce infection incidence

Agricultural policy:

• Restrict routine antibiotic use in healthy livestock
• Ban antibiotics as growth promoters in farming
• Improve animal welfare to reduce disease incidence

The challenge is that developing new antibiotics is expensive and time-consuming, whilst resistance can emerge within years. Pharmaceutical companies have limited financial incentive to invest in new antibiotics compared to treatments for chronic conditions.

Comparing vaccination and antibiotic treatment

Both strategies are essential for disease control. Vaccination reduces the need for antibiotics by preventing infections, which in turn reduces selection pressure for resistance.

Worked examples

Example 1: Explaining vaccine effectiveness (6 marks)

Question: A student was vaccinated against measles. Two years later, they were exposed to the measles virus but did not develop the disease. Explain why the vaccine prevented them from becoming ill.

Mark scheme answer:

• The vaccine contained dead/inactive measles virus [1 mark]
• White blood cells/lymphocytes detected antigens on the vaccine pathogen [1 mark]
• White blood cells produced antibodies specific to measles antigens [1 mark]
• Some white blood cells became memory cells [1 mark]
• When exposed to live measles virus, memory cells recognised the antigens [1 mark]
• Memory cells rapidly produced large quantities of measles antibodies that destroyed the virus before symptoms developed [1 mark]

Examiner note: Full marks require explanation of both the initial vaccination response AND the secondary response upon re-exposure.

Example 2: Antibiotic resistance (4 marks)

Question: Explain how the incorrect use of antibiotics can lead to the development of resistant bacteria.

Mark scheme answer:

• Random mutations in bacterial DNA produce some antibiotic-resistant bacteria [1 mark]
• When antibiotics are used incorrectly (e.g., not completing the course), some bacteria survive [1 mark]
• The resistant bacteria are selected for/have a survival advantage [1 mark]
• Resistant bacteria reproduce and pass on resistance genes, creating a resistant population [1 mark]

Examiner note: Questions often specify "incorrect use" — ensure you mention this in your answer, not just the mechanism of natural selection.

Example 3: Herd immunity (3 marks)

Question: In a school of 1000 students, 920 have been vaccinated against flu. Suggest why even unvaccinated students are less likely to catch flu than if only 500 students had been vaccinated.

Mark scheme answer:

• High vaccination rate creates herd immunity [1 mark]
• Vaccinated students cannot catch or spread flu to others [1 mark]
• This reduces transmission, so unvaccinated students have fewer opportunities to encounter the virus [1 mark]

Common mistakes and how to avoid them

• Confusing antibodies with antibiotics — Antibodies are proteins produced by your immune system; antibiotics are medicines that kill bacteria. Remember: antibodies are biological, antibiotics are chemical drugs.

• Thinking antibiotics work on viruses — Antibiotics only kill bacteria because they target bacterial structures (cell walls, ribosomes) that viruses lack. Always specify "bacterial infections" when discussing antibiotic use.

• Describing vaccines as "curing" disease — Vaccines prevent disease by creating immunity before infection occurs. Antibiotics treat existing bacterial infections. Prevention vs treatment is a key distinction.

• Incomplete explanations of antibiotic resistance — You must explain mutation, selection, reproduction and inheritance. Simply stating "bacteria become resistant" scores no marks without the mechanism.

• Forgetting the role of memory cells — In vaccination questions, explaining that antibodies are produced is insufficient. Memory cells enable the rapid secondary immune response that prevents disease symptoms.

• Vague descriptions of herd immunity — Specify that high vaccination rates protect unvaccinated individuals by reducing disease transmission in the population, not just that "most people are protected."

Exam technique for "Immunisation and Antibiotics"

• Command word "Explain" — Provide reasoning and mechanisms, not just descriptions. For 4–6 mark questions, structure your answer in logical steps showing cause and effect. Each sentence should advance your explanation.

• Use correct scientific terminology — Terms like "lymphocytes," "antigens," "antibodies," "memory cells," and "natural selection" demonstrate precise understanding and earn marks. Avoid vague terms like "germs" or "bugs."

• Link structure to function — When discussing why antibiotics don't work on viruses, reference specific structural differences (cell walls, metabolic machinery). When explaining vaccines, reference the antigen-antibody relationship.

• Read carefully for context — Questions may specify bacterial vs viral infections, correct vs incorrect antibiotic use, or primary vs secondary immune response. Your answer must address the specific scenario presented.

Quick revision summary

Vaccination introduces dead/inactive pathogens, stimulating white blood cells to produce specific antibodies and memory cells. This creates immunity by enabling rapid antibody production upon re-exposure, preventing disease symptoms. Herd immunity protects unvaccinated individuals when vaccination rates are sufficiently high. Antibiotics kill bacteria by targeting bacterial-specific structures but cannot treat viral infections. Antibiotic resistance develops through natural selection when resistant bacteria survive treatment and reproduce. Completing antibiotic courses, restricting unnecessary prescriptions, and developing new antibiotics help combat resistance.