How do vaccines protect us, and how are new drugs discovered and tested?
How vaccination produces immunity, the action of antibiotics and painkillers, the discovery of drugs, and the stages of preclinical and clinical testing including placebos and double-blind trials.
A focused answer to AQA GCSE Biology 4.3.1.3 to 4.3.1.6, covering how vaccination produces immunity, the action of antibiotics and painkillers, and the discovery, testing and trialling of new drugs.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
AQA wants you to explain how vaccination produces immunity, distinguish what antibiotics and painkillers do, describe how drugs were originally discovered, and outline the stages of testing and trialling a new drug, including placebos and double-blind trials.
How vaccination works
The key is that memory cells are made and remain in the body after vaccination, so the second response is fast and large. If a large proportion of the population is vaccinated, the spread of a pathogen is greatly reduced, even for those who are not vaccinated, because the pathogen has few people to infect. This is called herd immunity.
Antibiotics and painkillers
- Antibiotics (such as penicillin) kill bacteria inside the body and have greatly reduced deaths from bacterial diseases. They cannot kill viruses, because viruses live and reproduce inside the body's own cells, so a drug that killed them would damage the cells too. Specific bacteria are treated with specific antibiotics.
- Painkillers and other medicines treat the symptoms of a disease (such as pain or fever) but do not kill the pathogen.
Discovering and testing new drugs
Traditionally drugs were extracted from plants and microorganisms: digitalis (a heart drug) comes from foxgloves, aspirin originates from willow, and penicillin was discovered by Alexander Fleming from the Penicillium mould. Most new drugs today are synthesised by chemists, but the starting point may still be a chemical found in a plant or microorganism.
New drugs are tested in stages before they can be used:
- Preclinical testing: done in a laboratory using cells, tissues and then live animals, to check the drug's toxicity (is it harmful), efficacy (does it work) and the right dose.
- Clinical trials: done on healthy volunteers and patients. Very low doses are given first to check the drug is safe, then the optimum dose is found in patients.
Try this
Q1. Explain why a vaccine protects you against a disease. [3 marks]
- Cue. It contains dead or inactive pathogen; white blood cells make antibodies and memory cells; if the real pathogen invades, the body responds quickly.
Q2. Explain why antibiotics cannot be used to treat a cold. [1 mark]
- Cue. A cold is caused by a virus, and antibiotics only kill bacteria.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20184 marksExplain how a vaccine protects a person from becoming ill if they later meet the pathogen, and explain how vaccinating most of a population protects those who are not vaccinated.Show worked answer →
A 4-mark explain question rewards the immune mechanism plus herd immunity.
A vaccine contains a small amount of dead or inactive pathogen carrying antigens. White blood cells (lymphocytes) respond by producing antibodies, and memory cells are made and remain in the body. If the real, live pathogen later enters, the memory cells recognise the antigen and produce the correct antibodies very quickly and in large amounts, destroying the pathogen before it causes illness.
If most of the population is vaccinated, there are few people the pathogen can infect and reproduce in, so it cannot spread easily, which protects the unvaccinated too. This is called herd immunity.
Markers reward antigen leading to antibodies and memory cells, the rapid second response, and herd immunity reducing spread.
AQA 20214 marksA new drug is being developed. Describe the stages of preclinical and clinical testing, and explain why a double-blind trial using a placebo is used.Show worked answer →
A 4-mark question rewards the testing stages plus the reason for the trial design.
In preclinical testing the drug is tested in the laboratory on cells, tissues and then live animals to check for toxicity, efficacy (whether it works) and the correct dose. If it passes, clinical trials begin on human volunteers: a very low dose is given first to healthy volunteers to check it is safe, then it is tested on patients to find the optimum dose.
In a double-blind trial some patients receive a placebo (a dummy treatment) and neither the patients nor the doctors know who has the real drug until the results are analysed. This prevents bias, so the effect measured is due to the drug and not to expectations.
Markers reward preclinical (cells, tissues, animals) then clinical (healthy volunteers then patients), checking toxicity, efficacy and dose, and the placebo and double-blind design preventing bias.
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Sources & how we know this
- AQA GCSE Biology (8461) specification — AQA (2016)