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The advantages of immunisation are obvious - they stop individuals becoming ill. If enough people are immunised, immunisations can also stop pathogens infecting whole populations. This is called herd immunity.

There are also risks to having immunisations. For instance, some people suffer from a mild reaction to the vaccine.

In recent years there has been much controversy surrounding the MMR vaccine. Some people used to think the vaccine - which is a combined treatment against measles, mumps and rubella - could cause autism in children. They and hoped they would not catch measles, mumps or rubella.

But this meant that, as fewer and fewer children were immunised, the three diseases began to spread more easily and the number of cases began to increase. More recent studies by the World Health Organisation have shown that there is no link between the MMR vaccine and autism.

Immunisations can never be completely safe and there is always a risk of some side-effect. So, when making a decision, these are some of the factors that need to be considered:

• when fewer people are immunised, 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

Explore vaccinations, painkillers and antibiotics with Dr Alex Lathbridge.

Listen to the full series on ����ý Sounds.