Vaccines

Vaccines train the body to build immunity against infectious diseases without us having to catch the illness. They are one of the most effective ways to prevent serious disease.

How vaccines work#

Our immune system is made up of special cells and chemicals, including antibodies, that fight infection. We gain immunity against a disease either naturally, by catching the illness, or through vaccination.

Most vaccines contain a modified version of a disease-causing germ or toxin. These active ingredients are called antigens, and they are the most important part of any vaccine. An antigen may be:

• a live but weakened germ
• a dead germ
• a small part of a germ, such as a molecule from its surface
• an inactivated toxin produced by bacteria

Some vaccines work differently. mRNA vaccines instruct our cells to make a protein that triggers an immune response.

Vaccines are usually given by injection or, in some cases, as a small drink. The immune system responds to the antigen as if it were a fully active germ and makes antibodies to destroy it – all without us catching the illness.

The way each vaccine is designed depends on how the specific germ makes us sick. For example, tetanus is caused by the body’s reaction to a toxin produced by the tetanus bacteria, so the tetanus vaccine contains an inactivated form of that toxin.

How vaccines help our immunity#

Our immune system is like a library: it stores information about every germ it has ever defeated. We sometimes call this immunological memory.

Some antibodies stay “on patrol” in our bloodstream. If we encounter the real germ in the future, the immune system can quickly call on its memory cells and produce antibodies to defeat it – often before we notice any symptoms of illness.

Some vaccines offer lifelong immunity, while others need “catch-up” doses or booster shots to keep protection strong.

A short history of vaccines#

Immunisation is not new – the techniques were pioneered more than 200 years ago. At a time when smallpox was a feared and deadly disease, an eighteenth-century doctor named Edward Jenner noticed that farm workers who caught the mild illness cowpox seemed to be immune to smallpox.

Jenner reasoned that the cowpox germ was similar enough to the smallpox germ to “train” the immune system to defeat both diseases. He was correct, and immunisation today still relies on similar principles.

What is in vaccines?#

Ingredients vary depending on the infection, and they may change from year to year as new strains of a virus appear. As well as antigens, a vaccine may contain a small amount of:

• diluents, such as sterile water or saline
• preservatives or other ingredients to stop the vaccine becoming contaminated or going off

mRNA vaccines instead teach our cells how to make a protein that stimulates an immune response. Every ingredient is monitored for safety and effectiveness.

How new vaccines are developed#

Developing a new vaccine can take a long time. Vaccines pass through many stages, including research, discovery, pre-clinical testing, clinical testing and regulatory approval. Once approved, a vaccine is manufactured and shipped to where it is needed.

In some circumstances, extra resources, overlapping clinical trials and funding can speed up development. After a vaccine is introduced, it continues to be closely monitored through trials and surveillance to confirm it is effective and safe. Regional and national surveillance systems actively watch for any adverse events following immunisation, because unexpected side effects can occasionally appear once a vaccine is in wide use.

Some vaccines, such as the flu vaccine, need to be updated every year to respond to changing strains. For these updates the process is streamlined so the vaccine is available when needed.

Are vaccines safe?#

Vaccines are much safer than catching the disease. Vaccine-preventable diseases can cause lifelong complications or death, even in normally healthy people.

The safety of vaccines is sometimes questioned, but millions of people – many of them babies and young children – are immunised every year with no side effects. Most reactions are mild and usually last one to two days. Like any medication, vaccines carry a small degree of risk, but serious side effects are rare, and that small risk must be weighed against the risk of the disease itself.

For example, there is a very small risk of developing the rare condition idiopathic thrombocytopenic purpura (ITP) after the measles, mumps and rubella (MMR) or measles, mumps, rubella and varicella (MMRV) vaccine. However, the risk of developing ITP from a measles infection is many times greater than the risk from the vaccine.

How successful are vaccines?#

Vaccination is the most effective preventive measure against infectious diseases. Most vaccine-preventable illnesses are highly contagious, spread quickly and can cause severe complications that affect quality of life. Vaccines give us immunity without us getting sick.

They also protect vulnerable people in our community who cannot be immunised, such as very young children or those who are too sick. When enough people are vaccinated, the spread of a disease slows down or stops completely. We call this herd immunity, or community immunity.

The percentage of people who need to be immune to achieve herd immunity varies from one disease to another. For some highly contagious diseases, around 95 out of every 100 vaccinated people will be fully immune; for others, the figure may be closer to 85 out of every 100.

How long does a vaccine take to work?#

After we receive a vaccine, the immune system gets to work straight away creating antibodies and memory cells. On average, an immune response takes around 7 to 21 days. How long immunity lasts depends on several factors, including the type of vaccine, the timing of doses, our age, and whether we have had the infection naturally.

Which vaccines do we need?#

The vaccines we may need are determined by our health, age, lifestyle and occupation:

• Health – some people may benefit from additional or more frequent immunisations, for example pregnant women, premature babies, or people with conditions such as asthma, diabetes, HIV, or disorders of the heart, lungs, spleen or kidneys.
• Age – we are more vulnerable to certain illnesses at different ages, such as in childhood, during the school years and in older age.
• Lifestyle – some choices can put us or others at risk, such as overseas travel, becoming a new parent, sexual activity, smoking, or playing contact sport.
• Occupation – some jobs carry a higher risk of exposure to infection, such as work in hospitals, childcare and emergency services.

If you are not sure which vaccines you need, talk to your doctor or immunisation provider. If you are not up to date, your provider can arrange catch-ups and boosters. Recommended immunisation schedules set out the vaccines suggested for infants, children, older people and others at higher risk, and in many places recommended vaccines are provided at no cost to these groups.

Key points#

• Antigens are the most important ingredient of all vaccines.
• Vaccination is the most effective preventive measure against serious diseases.
• Some antibodies remain “on patrol” in our bloodstream.
• This protection often acts before we experience any symptoms of illness.
• Diseases that can be prevented by vaccines can cause lifelong complications or death, even in normally healthy people.

Where to get help#