Women's and Children's Hospital, Adelaide


What is immunisation?

Immunisation protects children and adults against harmful infections before they come into contact with them in the community. Immunisation uses the body's natural defence mechanism - the immune response - to build resistance to specific infections. Several diseases can be prevented by routine childhood immunisation including rubella, tetanus and poliomyelitis (polio). These diseases can cause serious complications and sometimes death.

Immunisation is given as an injection or, in the case of rotavirus vaccine, as liquid that is swallowed.

Immunisation helps children stay healthy by preventing serious infections.

How does immunisation work?

All forms of immunisation work in the same way. When someone is injected with, or swallows a vaccine, their body produces an immune response in the same way it would follow exposure to a disease but without the person getting the disease. If the person comes in contact with the disease in the future, the body is able to make an immune response fast enough to prevent the person getting sick.

What is in vaccines?

Some vaccines contain a very small dose of a live, but weakened form of a virus. Some contain a very small dose of killed bacteria or small parts of bacteria. Some contain a small dose of a modified toxin produced by bacteria.

Vaccines may also contain either a small amount of preservative or a small amount of an antibiotic to preserve the vaccine. Some vaccines may also contain a small amount of an aluminium salt which helps produce a better immune response.

How long do immunisations take to work?

Normally several weeks. This means protection from an infection will not occur immediately after immunisation. Most immunisations need to be given several times to give lasting protection. 

How long do immunisations last?

The protective effect of immunisations is not always life-long. Some can last up to 30 years, some, such as whooping cough, give protection for about five years after a full course.

Is everyone protected from disease by immunisation?

Even when all the doses of a vaccine have been given, not everyone is protected against the disease. Many vaccines protect more than 95% of children who have completed the course. Some protect around 85% of children, reducing the severity of the disease for the other 15%.

Why do children get so many immunisations?

A number of immunisations are required in the first few years of a child's life to protect them against the most serious infections of childhood. The immune system in young children does not work as well as in older children and adults, because it is still immature. Therefore more doses of the vaccine are needed.

In the first few months of life, a baby is protected from most infections by antibodies from their mother which are transferred to the baby during pregnancy. When these antibodies wear off, the baby is at risk of serious infections so the first immunisations are given before these antibodies have gone.

What are the side effects of immunisation?

Common side effects are redness and soreness where the injection was given and mild fever. While these symptoms might concern you and upset your child at the time, the benefit of immunisation is protection from the disease. Paracetamol might be needed to help ease the fever and soreness. Other side effects are very rare, but if they do occur, you should call your doctor immediately.

Why should I have my child immunised?

Immunisation is the safest and most effective way of giving protection against some diseases. After immunisation your child is far less likely to catch the disease if there are cases in the community. The benefit of protection far outweighs the very small risks of immunisation.

If enough people in the community are immunised, the infection can no longer be spread from person to person so the disease dies out altogether. This is how smallpox was eliminated from the world, and how polio has disappeared from many countries.


The Immunisation Calculator uses the Australian Standard Vaccination Schedule. It recommends doses of vaccine to be given at specific ages. If doses of vaccine are delayed or missed, the calculator will assist in providing a 'catch-up' schedule for future vaccine doses

For further information visit the Population Health SA website - a public and environmental health information resource maintained by the Environmental Health Service of the Department of Health.

For up to date and detailed information regarding immunisation we suggest the following

Australian Childhood Immunisation Register

National Health & Medical Research Council

Australian Department of Health & Ageing


Acknowledgment: Much of the above information is drawn from the booklet 'Understanding Childhood Immunisation' produced by the Commonwealth Department of Health and Aged Care.

last modified: 02 Dec 2011