Vaccines help reduce the risk of certain infectious diseases by introducing a modified version of the disease-causing organism to the person's immune system. Some vaccines offer lifelong immunity. In other cases, booster shots are needed. Serious side effects from vaccines are rare.
Vaccines help reduce the risk of a disease by introducing a dead or weakened version of the disease-causing germ (bacteria or virus) to the body’s immune system. If our immune system then encounters the ‘real’ disease-causing germ, quick recognition allows our body to fight infection with a rapid and effective immune response. In this way, vaccines mimic the body’s natural immunity.
Immunisation (vaccination) is the most effective preventative measure against infectious diseases. Some vaccines offer lifelong immunity. In other cases, booster shots are needed.
Serious side effects from vaccines are rare and much less common than the serious effects of the disease. Some diseases, such as poliomyelitis or diphtheria, can be so destructive that the infected person may suffer lifelong complications or even die.
How vaccines work
The human immune system is made up of special cells and chemicals that fight infection. The human body can gain immunity against certain diseases either naturally (by catching and surviving, or coming into contact with, the illness) or through immunisation.
Vaccines work by introducing a modified version of a disease-causing microbe (germ) to the immune system. People are usually given an injection or a small drink (that contains the vaccine). Depending on the disease, the vaccine could be a weakened or dead microbe, or a part of the microbe (for example, its protein wall). In other cases, where the disease is caused by toxins (poisonous substances) produced by bacteria, the vaccine contains the weakened toxin.
The immune system responds to the weakened, partial or dead microbe as if it was a fully-fledged germ and makes antibodies to destroy it. These antibodies are made without the person getting sick.
Later, some of these antibodies remain ‘on patrol’ in the bloodstream and can increase quickly if the germ is encountered. This means that the key to defeating that particular disease is stored long term (known as immunological memory).
Vaccines mimic natural immunity
A person’s natural immunity is like a library and contains information on every germ ever defeated by their immune system. If the person encounters the real disease-causing germ in the future, their immune system will know how to defeat it, often before the person experiences any symptoms of illness. This explains why (in most cases) diseases such as mumps and rubella (German measles) are only detected once, even though exposure to the virus may be repeated throughout life.
Vaccines are designed according to how particular germs make you sick. For example, measles is the result of the body’s reaction to the whole virus. However, in tetanus, the body reacts to the toxin produced by the tetanus germ, rather than the germ itself.
Immunisation and health, age, lifestyle and occupation (HALO)
The immunisations you may need are decided by your health, age, lifestyle and occupation (HALO).
HALO is defined as:
- Health – some health conditions or factors may make you more vulnerable to vaccine-preventable diseases. For example, babies born prematurely, or people who have asthma, diabetes, heart, lung, spleen or kidney conditions, Down syndrome and HIV may benefit from additional or more frequent immunisations.
- Age – at different ages you need protection from different vaccine-preventable diseases. Australia’s National Immunisation Program sets out recommended immunisations for babies, children, older people and other people at risk, such as Aboriginal and Torres Strait Islander people. Most recommended vaccines are available at no cost to these groups.
- Lifestyle – lifestyle choices can have an impact on your immunisation needs. If you are travelling overseas to certain locations, planning a family, are sexually active, smoke, or play contact sport that may expose you directly to someone else’s blood, you may benefit from additional or more frequent immunisations.
- Occupation – you are likely to require additional or more frequent immunisations if you work in an occupation that exposes you to vaccine-preventable diseases, or puts you in contact with people who are more susceptible to problems from vaccine-preventable diseases such as babies or young children, pregnant women, the elderly, and people with chronic or acute health conditions. Workers in aged care, childcare, healthcare, emergency service, or sewerage repair and maintenance, need to discuss their immunisation needs with their doctor. Some employers help with the cost of relevant vaccinations for their employees.
History of immunisation
Immunisation techniques were pioneered over 200 years ago, when smallpox was a feared and deadly disease. An eighteenth century doctor named Edward Jenner noted that farm labourers who contracted the mild disease cowpox were immune to smallpox. Jenner guessed that the germ responsible for cowpox was similar enough to the smallpox microbe to ‘train’ the immune system to defeat both diseases. He was correct. Immunisation today relies on similar principles.
No vaccine is completely effective
Out of 100 people immunised against a particular disease, about five to 15 will catch the disease if they are exposed to it. This may be because their immune systems didn’t respond to the vaccine and failed to make antibodies, or the vaccine may not have been stored correctly at the clinic.
However, if 100 people who have never had measles or never received the measles vaccine were exposed to the disease, almost every single one of them would catch it. Immunisation greatly reduces the risk of catching a disease, which in turn reduces the risk of complications.
Comparing the risks of vaccines
From time to time, the safety of vaccines has been questioned. Like any other medicine, vaccines carry a small degree of risk, but serious side effects are very rare. The risk of serious side effects must be weighed against the risk of the disease. For example, the risk of encephalitis (inflammation of the brain) from the measles, mumps, rubella (MMR) vaccine is thought to be just one in a million immunisations. However, according to some estimates, the risk of encephalitis from catching the mumps virus is one in 200.
Immunisation success stories
Immunisation is the most effective preventative measure against infectious diseases. Some recent immunisation success stories in Victoria include:
- Meningococcal C disease – from a peak of 88 cases in 2002, the number of cases has fallen every year since the introduction of meningococcal C vaccine in 2003. In 2010, there was only one case notified in Victoria.
- Haemophilus influenzae type b (Hib) disease – since immunisation against Hib disease was introduced in Victoria in 1993, cases among children under four years of age have dropped by more than 99 per cent. For 1991 and 1992, there was an average of 110 cases per year. This fell to less than one case per year for the period between 2000 and 2010.
- Measles – measles rates have been decreasing since 1969 when the vaccine became available in Australia. The most significant impacts have been from its inclusion on the National Immunisation Program in 1983, the introduction of a second measles vaccine dose in 1994 and a primary school Measles Control Campaign in 1998. In Victoria, the average number of measles cases has decreased from 75 cases per year between 1997 and 1999 to an average of 11 cases per year between 2005 and 2010. The most common group of people seeking treatment for measles since 2000 (more than two thirds of cases) are those who were born after 1966 (who were not exposed to the pre-vaccine era of large outbreaks) and people born before 1982 (who were not vaccinated or only received one dose). The majority of these people have contracted measles during overseas travel.
Australia’s National Immunisation Program
The National Immunisation Program sets out recommended immunisations for infants, children, older people and other people at risk, such as Aboriginal and Torres Strait Islanders. Most recommended vaccines are available at no cost to these groups. If you need further information, talk to your doctor.
Where to get help
- Your doctor
- Your local council immunisation service
- Maternal and child health nurse
- NURSE-ON-CALL Tel. 1300 606 024 – for expert health information and advice (24 hours, 7 days)
- Department of Health Victoria Immunisation, Tel. 1300 882 008
- Immunise Australia Program Tel. 1800 671 811
Things to remember
- Vaccines help reduce the risk of certain infectious diseases by introducing dead or weakened versions of disease-causing germs (bacteria or viruses) to the immune system.
- Some vaccines offer lifelong immunity.
- Immunisation greatly reduces the risk of catching a disease, which in turn reduces the risk of complications.
You might also be interested in:
- Chickenpox - immunisation.
- Haemophilus influenzae type b (Hib).
- Hepatitis B - immunisation.
- Immune system.
- Immunisation - childhood.
- Immunisation - facts and misconceptions.
- Immunisation - teenagers.
- Immunisations - catch-ups.
- Meningococcal disease - immunisation.
- Polio - immunisation.
- Q fever.
- Travel vaccinations.
- Whooping cough.
Want to know more?
Go to More information for support groups, related links and references.
This page has been produced in consultation with and approved by:
(Logo links to further information)
Department of Health logo
Last reviewed: October 2012
Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.
Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your qualified health professional. Content has been prepared for Victorian residence and wider Australian audiences, and was accurate at the time of publication. Readers should note that over time currency and completeness of the information may change. All users are urged to always seek advice from a qualified health care professional for diagnosis and answers to their medical questions.
For the latest updates and more information, visit www.betterhealth.vic.gov.au
Copyight © 1999/2013 State of Victoria. Reproduced from the Better Health Channel (www.betterhealth.vic.gov.au) at no cost with permission of the Victorian Minister for Health. Unauthorised reproduction and other uses comprised in the copyright are prohibited without permission.