Antibiotics and drug testing

Vaccination involves exposing the body’s immune system to a weakened or harmless version of the pathogen in order to stimulate white blood cells to produce antibodies. Antibiotics are used to treat bacterial infections. Bacteria can mutate and become resistant to antibiotics. This is one reason why new drugs are constantly being developed.


People can be immunised against a pathogen [pathogens: microorganisms that cause disease ] through vaccination. Different vaccines are needed for different pathogens.

Vaccination involves putting a small amount of an inactive form of a pathogen into the body. Vaccines can contain:

  • live pathogens treated to make them harmless
  • harmless fragments of the pathogen
  • toxins [toxins: a type of natural poison produced by an organism, often as a form of protection ] produced by pathogens
  • dead pathogens.

These all act as antigens [antigens: Foreign organisms that get into the body, and trigger an immune response. ]. When injected into the body, they stimulate white blood cells to produce antibodies to fight the pathogen.

The vaccine contains only a weakened or harmless version of a pathogen, which means that the vaccinated person is in no danger of developing the disease. Some people, however, may suffer a mild reaction. If the person later becomes infected with the pathogen, the required (white blood cells) are able to reproduce rapidly and destroy it.

Vaccines and boosters

Vaccinations in early childhood can offer protection against many serious diseases. Sometimes more than one vaccine is given at a time, like the MMR triple vaccine against mumps, measles and rubella.

Sometimes vaccine boosters are required because the immune response ‘memory’ weakens over time. Anti-tetanus injections may need to be repeated every ten years, for example.

Ideas about science - making decisions

There is often a conflict between a person’s right to decide what is best for themselves and their family and what is best for society as a whole. For example, some people used to think the MMR (measles, mumps or rubella) vaccine could cause autism in children. They decided not to risk letting their child have the vaccine and hoped they would not catch any of the three diseases. But this meant that as less and less children were vaccinated the diseases began to spread more easily and the number of cases began to increase. Therefore, a decision originally taken by a number of single individuals had big implications for society as a whole.

Vaccinations can never be completely safe because side-effect levels vary. So, when making a decision, these are some of the factors that should be considered:

  • when fewer people are vaccinated, the number of cases of the disease increases
  • the chance of falling seriously ill or dying from the disease may be far greater than the chance of experiencing a serious side-effect
  • using a vaccine may be much cheaper than treating a very ill person.

Some issues with vaccination


spherical shaped virus showing a cross-section through the core

A hepatitis C virus showing DNA enclosed in a protein coat.

Some common diseases like influenza (flu) and the common cold are caused by viruses. These mutate quickly, and this changes their surface proteins. This makes it almost impossible to develop a permanent vaccine [Vaccines: substances containing disabled antigens of a particular disease, usually administered via injection. Vaccines stimulate the body to produce antibodies to provide immunity against that disease. ] against them. A new flu vaccine has to be developed every year, after the strain has been analysed.

There is no vaccine for the common cold because the virus that causes it mutates far too quickly. By the time a vaccine could be developed, the virus would have changed its surface proteins and would no longer be recognised by the antibodies [antibodies: Proteins produced by the body's immune system that attack foreign organisms (antigens) that get into the body. ].



You may wish to view this BBC News item (2006) about the recommendation that pregnant women should be offered the flu vaccine in winter.

The government has policies on vaccination which advises which stage in their life people should be vaccinated against different diseases. The policies and advice are updated as and when new scientific information becomes available.

Ideas about science - weighing up arguments

With respect to vaccination policies, you need to be able to:

  • Clearly state the issue. For example, is the risk of suffering side-effects from the vaccination greater or less than the risk of catching the disease?
  • Summarise different views that might be held. For example, some people used to think there was a risk of children developing autism when they had the MMR vaccine. Other people thought the MMR vaccine was safe and there was no risk of developing autism.
  • Identify and develop arguments based on the idea that the right decision is the one that leads to the best outcome for the majority of people. For example, even though there may be a slight risk from being vaccinated, society as a whole will benefit because it will help to reduce the risk of the disease being passed on to other people.
  • Identify and develop arguments based on the idea that certain actions are very hard to justify because they are considered unnatural or wrong. For example, most people think governments should not pass laws making vaccination compulsory, because that would take away our human right to freedom of choice.


During an epidemic, an infectious disease such as influenza spreads very quickly. Epidemics can be prevented if a high proportion of the population has been vaccinated. This reduces the number of people who are able to catch the disease and pass it on to others. The more infectious the disease, the higher the proportion of the population that must be vaccinated to prevent the epidemic.

Ideas about science - feasibility

With respect to vaccination policies, you need to be able to distinguish what can be done, ie what is technically feasible, from what should be done. For example, smallpox is the only disease that has been eradicated from the planet by vaccination. This was possible because smallpox is spread by direct contact, and not through the air.

This made it possible to vaccinate enough people in the world to completely stop the disease from spreading.

Some other diseases are more infectious but if we could vaccinate a sufficient number of the world’s population we could, in theory, eliminate the disease. However, at the moment this is not technically feasible because we do not have enough vaccine, some areas of the world are at war and inaccessible, and some people would refuse to be vaccinated.


Antibiotics are substances that kill bacteria [bacteria: Single-celled microorganisms, some of which are pathogenic in humans, animals and plants. Singular is bacterium. ] or prevent their growth. They do not work against viruses [viruses: ultramicroscopic non-cellular organisms that replicate themselves inside the cells of living hosts ]. It is difficult to develop drugs that kill viruses without damaging the body’s tissues.


A bacterium damaged and distorted by penicillin

The first antibiotic, penicillin, was discovered by Alexander Fleming in 1928. He noticed that some bacteria he had left in a Petri dish had been killed by naturally occurring penicillium mould.

Since the discovery of penicillin, many other antibiotics have been discovered or developed. Most of those used in medicine have been altered chemically to make them more effective and more safe for humans.

Antibiotic resistance

Over time, bacteria [bacteria: Single-celled microorganisms, some of which are pathogenic in humans, animals and plants. Singular is bacterium. ] can become resistant to certain antibiotics [antibiotics: Substances that kill bacteria. ]: this is an example of natural selection. In a large population of bacteria, there may be some that are not affected by the antibiotic. These survive and reproduce, creating more bacteria that are not affected by the antibiotic.


Mutations in bacteria can result in them becoming resistant to antibiotics, turning the bacteria into a ‘superbug’. Superbugs can develop while a person is taking a course of antibiotics.


MRSA is methicillin-resistant Staphylococcus aureus. It is very dangerous because it is resistant to most antibiotics. To slow down or stop the development of other strains of resistant bacteria, we should:

  • always avoid the unnecessary use of antibiotics
  • always complete the full course



You may wish to view this BBC News item (2007) about how drug-resistant strains of TB are putting European Union states at risk of a deadly outbreak.

Tuberculosis (TB), is a disease caused by a bacterium called Mycobacterium tuberculosis. Most people who are infected do not show any symptoms. But about 10 per cent go on to develop serious symptoms including shortness of breath, coughing, fever and even death.

Infected people without symptoms are usually given a course of one antibiotic [antibiotics: Substances that kill bacteria. ]. Those who show symptoms need a course of several antibiotics at once. This is to reduce the chance of strains of antibiotic-resistant bacteria emerging.

Development of resistance - Higher tier

The main steps in the development of resistance are:

  1. Random changes or mutations occur in the genes of individual bacterial cells
  2. Some mutations protect the bacterial cell from the effects of the antibiotic
  3. Bacteria without the mutation die or cannot reproduce with the antibiotic present
  4. The resistant bacteria are able to reproduce with less competition from normal bacterial strains

Drug testing

Drugs and their origins

Drugs are substances that cause changes to the body. Some can help the body, others can harm it.

Certain drugs can be extracted from natural sources and their existence has been recognised for a long time. For example, willow bark was used by the ancient Greeks to help cure fevers and pains. It was later discovered that the active ingredient was salicylic acid. This was modified by chemists into the substance we call aspirin, which is less irritating to the stomach than salicylic acid.

salicylic acid and aspirin molecules

Three stages of testing drugs

New medical drugs have to be tested to ensure that they work, and are safe, before they can be prescribed. There are three main stages of testing.

  1. The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work.
  2. Drugs that pass the first stage are tested on animals. In the UK, new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects.
  3. Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check they are safe. The substances are then tested on people with the illness to ensure they are safe and that they work.

Medical drug trials


You may wish to view this BBC News item (2006) about a drug trial that left six volunteers very ill.

Medical drug trials are not without risk. Sometimes severe and unexpected side-effects occur.

Most substances do not pass all of the tests and trials, so drug development is expensive and takes a long time.

Read on if you are taking the higher paper.

Human trials - Higher tier

It is important that the results of clinical trials are not influenced by the expectations of the people involved. So volunteers are put into two groups at random. Checks are done to make sure both groups have a similar gender balance and age range.

There are three main types of clinical trial: 'blind', 'double-blind' and 'open-label'. In blind and double-blind trials one group of volunteers, called the test group, receives the new drug. Another, the control group, receives the existing drug for that illness. If there is no existing treatment, the control group is given a fake drug that has no effect on the body. This is called a placebo. The researchers look for differences between the experimental group and the control group. In an open-label trial there are some differences.

Blind trials

In a blind trial, the volunteers do not know which group they are in but the researchers do. The problem is the researchers may give away clues to the volunteers without realising it. This is called observer bias; it can make the results unreliable.

Double-blind trials

In a double-blind trial, the volunteers do not know which group they are in, and neither do the researchers, until the end of the trial. This removes the chance of bias and makes the results more reliable. But double-blind trials are more complex to set up.

Open-label trials

In an open-label trial the patient and doctor both know the treatment. This type of trial happens when there is no other treatment and the patients are so ill that doctors believe they will not recover from their illnesses.


Many doctors do not like giving a placebo to patients with a disease because they feel the patient will not benefit from taking a fake drug and will not get better. They do not think this is fair to the patient.

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