Health and disease, Year 10: vaccination, antibiotics and new medicines

Their white blood cells make the correct antibodies quickly

HintThe body has seen this pathogen before, in a safe form. Think about how that changes the speed of its response.

The whyThe first time the body meets a pathogen, making the right antibodies takes days, and the pathogen has time to cause illness. After vaccination the response is fast enough to destroy the pathogen before it can do so.

The pathogen cannot spread through the population to reach the baby

HintA disease passes from person to person. Picture its route when almost everyone it meets is immune.

The whyWhen a large proportion of a population is immune, an infected person is unlikely to pass the pathogen on, so outbreaks die out. People who cannot be vaccinated are protected by those around them.

The antibodies made fit only the measles pathogen

HintThink of a key cut for one lock.

The whyAntibodies are specific: each kind matches one kind of pathogen. A vaccine contains a dead or inactive form of one pathogen, so the white blood cells learn to make the antibodies for that pathogen only.

vaccine

HintOne of them has to be in place before the pathogen arrives.

The whyA vaccine prepares the white blood cells in advance, so it is given before infection. An antibiotic kills bacteria that are already in the body, so it is given to someone who is ill.

The pathogen in it is dead or inactive

HintThink about the state of the microorganism that goes into the syringe.

The whyA vaccine contains a small quantity of a form of the pathogen that cannot reproduce and cause the illness. It still carries the features that white blood cells recognise, so antibodies are made without the disease.

symptoms

HintA headache, a fever and a sore throat are all examples.

The whyMedicines such as paracetamol make a person feel better while the body's own immune system deals with the infection. The pathogen is still there until the white blood cells, or another medicine, destroy it.

Viruses live inside the body's cells, so a drug that harms them may damage body tissue too

HintRemember where a virus hides while it reproduces.

The whyBacteria live as separate cells, so an antibiotic can attack them without touching our own cells. A virus reproduces inside a body cell, which makes it very hard to destroy the virus and leave the cell unharmed.

An antibiotic

HintPenicillin is the best-known example.

The whyAntibiotics have greatly reduced deaths from infectious bacterial diseases. They have no effect on viruses, so they are not used for viral infections such as colds, flu or measles.

Each antibiotic works against only some kinds of bacteria

HintDifferent medicines of this type have different targets.

The whyIt is important that specific bacteria are treated with specific antibiotics. The wrong one may not kill the bacteria causing the illness, so the patient stays ill and the bacteria have more chance to become resistant.

Infections they cause can no longer be cured with those antibiotics

HintImagine a serious illness for which the usual medicine has stopped working.

The whyResistant strains are not killed by an antibiotic that used to work. As more strains become resistant to more antibiotics, diseases that were once easily cured become dangerous again, which is why new antibiotics are needed.

The foxglove

HintA tall garden and woodland plant with a spike of purple, bell-shaped flowers.

The whyTraditionally, drugs were extracted from plants and microorganisms. Digitalis, used to treat heart conditions, comes from this plant, whose Latin name is Digitalis.

willow

HintThe tree grows beside rivers, and one kind is said to 'weep'.

The whyPeople used the bark of this tree to ease pain and fever for thousands of years. Chemists later worked out the active chemical and made a gentler version of it, which became aspirin.

Fleming

HintHis first name was Alexander, and he worked at St Mary's Hospital in London.

The whyHe noticed that bacteria were not growing around a mould that had got onto one of his culture plates. The mould was making a substance that killed bacteria, which he named penicillin.

Chemists in the pharmaceutical industry synthesise them

HintThink of a laboratory and a factory, not a garden.

The whyMaking a drug in a laboratory gives a pure product in large amounts, and lets its structure be adjusted to work better or cause fewer side effects.

A chemical extracted from a plant

HintRemember where digitalis and aspirin began.

The whyChemists often begin with a natural substance that is known to have an effect on the body, then copy or modify it. So even a synthetic drug can have a natural origin.

Toxicity, efficacy and dose

HintIs it harmful? Does it work? How much should be given?

The whyA new medicine has to be safe, it has to do its job, and the right amount to give has to be known. Testing and trialling check all three before the drug can be used.

Cells, tissues and live animals

HintThis stage happens in a laboratory, before any person takes the drug.

The whyPreclinical testing shows whether a substance is toxic and whether it has the intended effect, first on cells and tissues and then on a whole living body, before the risk is taken of giving it to people.

To check that the drug is safe before larger amounts are given

HintThe first question about any new medicine is whether it does harm.

The whyClinical trials use healthy volunteers and patients. If the low doses cause no harm, further trials are carried out to find the optimum dose: the amount that works best with the fewest side effects.

A placebo

HintThe word is Latin for 'I shall please'.

The whyIn a trial, some patients receive the drug and others receive the dummy. Comparing the two groups shows whether any improvement is really caused by the drug, and not by the patients' expectation of getting better.

Neither the patients nor their doctors

HintThe word 'double' tells you how many groups of people are kept in the dark.

The whyIf patients knew, their expectations could change how they feel; if doctors knew, it could influence how they judge the results. Keeping both unaware removes bias. Results are then published only after other scientists have checked them (peer review).