Frequently Asked Questions

Your questions about immunisation and vaccine-preventable diseases.

  • How do vaccines work?

    The basic idea behind a vaccine is to mimic a specific disease. Different vaccines protect against different diseases.

    Diseases are caused by things called pathogens, and the immune system is designed to protect the body from getting sick because of these pathogens. These pathogens contain antigens and these antigens are what cause the immune system to respond. Vaccines imitate the antigens found on the pathogens which cause the immune system to develop defences against that disease. It’s somewhat like a “wanted” poster – after vaccination, the immune system “knows” what to look for and so when it “sees” that specific pathogen it’s able to respond quickly to get rid of the pathogen before it causes disease.

    Further information can be found here:

    How Do Vaccines Work?

    How Vaccines Work

  • What is an antigen?

    An antigen is a substance which causes the immune system to produce antibodies. Antigens could be toxins, bacteria, viruses, chemicals or even pollen.  In a vaccine, it is usually a bacteria or virus (or part of a bacteria or virus) that teaches the body how to recognise the actual virus and how to produce antibodies against that antigen.

    Different types of vaccine antigens:

    • Attenuated live viruses: These vaccines have had the natural or “wild” virus treated and weakened so that it can trigger an immune response without causing the actual disease. Generally, one to two doses of this type of vaccine provides lifelong immunity to the specific disease the vaccine targets.
    • Inactivated viruses: These vaccines are made with the virus or part of the virus which has been inactivated through a chemical process. The virus is essentially “dead” and cannot reproduce or replicate to cause disease. However it still keeps its original form and therefore the immune system is able to recognise it and develop an immune response. Generally multiple doses of the vaccine are needed for long-lasting immunity.
    • Sub-unit vaccines: The part of the virus or bacteria which is identified as inducing immunity is separated from the part of the pathogen which causes disease.
    • Toxoid vaccines: Some bacteria cause disease through the release of a toxin. This toxin can be isolated and inactivated, with the resulting toxoid unable to cause disease but still able to stimulate an immune response.

    Further information can be found here:

    NLM Article

    Vaccines History

    What are Vaccines

    How Are Vaccines Made?

    Types of Vaccines

  • What is an antibody?

    An antibody is produced by the immune system in response to an antigen, and they neutralise the effects of an antigen by attaching to it. Antibodies are made in response to specific antigens.
    Further information can be found here:


  • What is the immune system?

    The immune system is a complex system including organs, specific cells and tissues which helps a body fight off threats from disease or other attack. The immune system remembers how it defended the body from the disease or other attack so that if it happens again, the body can fight back faster and stronger.

    Further information can be found here:

    Better Health – Immune System Facts
    Kids Health – Immunity
    Live Science – Immune System

  • What are the ingredients in a vaccine?

    Different vaccines contain different ingredients, but all contain an active ingredient, called an antigen [hyperlink to antigens]. Some vaccines contain only one antigen, whilst others contain multiple antigens. These antigens are modified from their original form in order to produce an immune response without causing illness.

    In addition to the antigen, vaccines contain adjuvants, stabilisers, diluents, and may also contain preservatives and trace components. Adjuvants are included to improve the immune response to the vaccine, and include aluminium salts such as aluminium phosphate, aluminium hydroxide, and potassium aluminium sulphate. By using an adjuvant, less antigen is required per vaccination, and for some vaccines can reduce the number of doses required. Only a very small amount of the adjuvant is included in the vaccine and is much less than what is found in a normal diet. A diluent is usually sterile saline or water and is used to dilute a vaccine in order to reach the correct concentration before it is administered.

    Stabilisers are utilised to keep the vaccine components stable whilst in storage, in order to keep a vaccine effective. They are used to stop the components sticking to the vial, and include lactose and sucrose, glycerine and monosodium glutamate, and human or bovine serum albumin. Some vaccines may include gelatine. Preservatives are included in some vaccines to keep the contents free of fungal and/or bacterial contamination. Preservatives were originally used to keep multi-vial vaccines free of contamination, but these types of vaccines are not generally used in Australia. Preservatives used include thiomersal, phenoxyethanol and phenol. Most vaccines used in Australia do not contain these preservatives.

    Trace components are minute amounts of substances which may have been used in the manufacturing process, such as cell culture fluids, egg proteins, yeast, antibiotics or agents used for inactivation. The production methods used such as filtering and centrifugation reduce the amounts of these products present in the final vaccine which is administered, but there may still be minute amounts present in the final product.

    Further information can be found here:

    Vaccine Components
    Vaccine Ingredients

  • How do we know vaccines work?

    A wide range of scientific studies have shown that in vaccinated populations, the diseases vaccinated against are found at much lower levels than in unvaccination populations. Whilst deaths from vaccine preventable diseases were generally declining before the introduction of specific vaccines, the actual incidence or infection rate of the disease wasn’t decreasing. Deaths were reducing due to improved treatments, better hygiene, higher standards of living and introduction of better medications. When the case (‘incidence’ or ‘morbidity’) rate is graphed over time, and the timing of the introduction of the vaccine is pinpointed, it can clearly be seen that rates of infection dramatically reduce.

    Because vaccines are designed to prevent infection, not to treat it, infection or case rates are the appropriate source to look at to see if the vaccine has helped to reduce the disease. Death, or mortality, rates don’t accurately reflect how widespread or how devastating a disease is – survivors can be left with lifelong complications such as paralysis (polio), deafness or sterility (mumps) or neurological complications (measles).

    Further information can be found here:

    Visual Vaccines – How Vaccines Work

    Vaccines – Graphs and Data

  • Diseases were decreasing before vaccines, weren’t they?

    Before the widespread use of vaccinations, death rates from the diseases we vaccinate against were generally dropping. This is related to better medical care, including the use of antibiotics and antiseptics, along with improved sanitation and nutrition rates. But what this doesn’t consider is the fact that people were still getting the disease – they just weren’t dying from it.

    Polio, for example, led to paralysis and often, eventually, death, before technology such as the iron lung was able to keep people with polio alive until they were able to recover from the virus. Once the first polio vaccine was introduced, both deaths (mortality) and actual cases (morbidity) reduced dramatically.

    The best example of how vaccines reduced the incidence of diseases is probably the chicken pox. This vaccine was introduced in Australia in 2000 and was funded for 18 month old children from 2005. This is a period of history with excellent sanitation and nutrition rates. Before the vaccine was used, Australia saw around 240,000 cases a year, with about 1,500 people hospitalised and around 7-8 deaths a year. Since the vaccine was introduced, declines of up to 73% in hospitalisation rates due to chicken pox have been seen in those under 40, with the biggest reduction in children aged between 1 and 4 years old.

    The best measure of whether a disease was decreasing before a vaccine was introduced is the case or morbidity rate, rather than the mortality rate. Many of these diseases can have serious, long term side effects beyond death, so for vaccine preventable diseases, prevention is definitely better than the cure.

    Further information can be found here:

    Top 20 Vaccine Questions
    Death Rates
    Immunise Health Handbook

  • How safe are vaccines?

    Vaccines are among one of the most studied and tested medications. In order for them to be provided in Australia under the National Immunisation Program, they must pass extremely strict and robust testing and registration programs in the world.

    Vaccines are subject to safety testing and ongoing monitoring. This means that if any issues following vaccination (also known as Adverse Events Following Immunisation (AEFI) are identified, that any patterns can be spotted and action taken swiftly. Adverse effects can be reported here. Vaccines are tested for a number of years before they are licensed for general use. There are several stages of clinical trials which a vaccine must pass through before it’s recommended for widespread use. This process can take a long time – up to 20 years. Clinical trials involve thousands of people and any adverse effects are noted and investigated. Many promising vaccinations (and other medicines) don’t pass these clinical trials and don’t make it onto the market.

    People can and do have adverse reactions to vaccination. In the majority of these cases, the reaction is mild and goes away quickly – for example, a slight fever, a sore arm, or body aches after vaccination. Some reactions are more severe, such as anaphylaxis (a serious allergic reaction), but these are extremely rare and immunisation providers are aware that they can occur, and take precautions so that if something like anaphylaxis does happen, they are able to respond quickly to help the person.

    Further information can be found here:

    Vaccine Safety
    Vaccine Safety
    Pediatric Publications – Vaccines

  • How can you still contract the disease if you’ve been vaccinated?

    Vaccines are more like a bullet proof vest than a force field – you can still get shot if you’re wearing a bulletproof vest, but you’re much less likely to be seriously injured or die if you’re shot in the vest. Vaccination helps your body know how to fight off the disease so that you have a better chance of defending yourself against the infection without getting as seriously sick as you probably would have had you contracted the disease without being vaccinated.

    Immunity to some diseases (like whooping cough) isn’t lifelong even if you get the actual disease, so it’s very hard for a vaccine to give you long lasting immunity. If you come into contact with the disease and your immunity from the vaccination has worn off, you’re more likely to get sick than if your immunity is still high from a recent booster. However, other vaccinations, such as for measles, are much more likely to give long term immunity and people who have been vaccinated according to the schedule are much less likely to contract measles than those who haven’t been vaccinated.

    Some people don’t develop immunity following vaccination. Often the only way to know this is through having a blood test to check immunity levels for some diseases, or if you actually get sick even though you’ve been vaccinated.

    Further information can be found here:

    Top 20 Questions About Vaccines

    Why you can still get a disease even if you are vaccinated

  • What vaccines should I consider if I’m considering pregnancy?

    If you are thinking about having a baby, it’s a good idea to check what  you have previously been immunised against, and having a blood test to check immunity levels specifically for hepatitis B, measles, mumps, rubella and chickenpox. Rubella and chickenpox can be especially dangerous for pregnant women, particularly in the first trimester, and can lead to serious complications for the baby. If you don’t have immunity to these diseases, it’s a good idea to get a booster at least a month before you start trying for a baby. The flu vaccination should also be considered for women planning a pregnancy.

    Depending on your lifestyle and general health, other vaccinations may also be recommended before considering a pregnancy, such as pneumococcal. It’s a good idea to talk to your doctor before you try for a baby to help get the best advice for your personal situation.

    Further information can be found here:

    Immunise Health Handbook
    Pregnancy and Vaccines
    Immunisation and Pregnancy

  • What vaccines should I consider if I’m pregnant?

    If you are currently pregnant, both the flu vaccination and the whooping cough vaccination are recommended for all pregnant women to protect themselves and their new baby against these diseases. The flu vaccination is recommended to be given at any stage of pregnancy, particularly if your second or third trimester will fall during the flu season. The whooping cough (pertussis) vaccination is recommended from 28 weeks on, with the optimal window being 28-32 weeks, although it can be given up until delivery. Ideally, the whooping cough vaccination is recommended to be given at least 2 weeks before delivery to allow enough time for antibodies to pass to the baby to offer protection until the baby is able to have its own vaccinations.

    In certain circumstances, additional vaccinations may be recommended to pregnant women. This would need to be discussed with your doctor.

    Further information can be found here:

    Vaccination and Pregnancy Fact Sheet
    Immunise Health Handbook

  • Can vaccines cause autism?

    Put simply, no – vaccines do not cause autism. Studies of millions of children have not found a link between vaccination and the development of autism.

    There are a number of reasons that some people believe there to be a link between vaccination and autism. One is that often parents first notice that a child has autistic tendencies at the same time as which they are getting their routine vaccinations. It is important to remember that just because something occurs at the same time or shortly after another event, it doesn’t mean the two events are related. Major studies of many, many children worldwide, has seen no increase in autism between vaccinated and unvaccinated populations.

    Another is that there has been an increase in the number of children diagnosed with autism, and the number of vaccinations given in childhood is also increasing. However, the diagnostic criteria for diagnosing autism have changed over the years, and now conditions that would have been diagnosed differently in the past now fall under the Autism Spectrum Disorder. Conversely, diagnoses which were previously used (such as language disorders) are used much more rarely as they now come under the diagnosis of ASD.

    A further reason is a study undertaken in 1998 which has since been retracted. This study looked at 12 children and concluded there was a link between the MMR vaccine, inflammatory bowel disease, and autism. There were significant concerns about the paper and ten of the thirteen authors have since retracted the conclusions of the paper. The journal which published it also issued a retraction and the lead author of the paper had his licence to practice medicine revoked.

    Other studies have linked the thiomersal (a mercury compound, used as an antiseptic or antifungal) in vaccinations to autism. However, thiomersal (or thimerosal) has not been present in childhood vaccinations in Australia since 2000, with only the Japanese encephalitis and Q fever vaccinations containing thiomersal (although one Hepatitis B vaccination, Engerix-B, contains trace amounts of it at such low levels that it is considered negligible). The removal of thiomersal has not seen a reduction in autism rates, which would be expected if thiomersal was linked to the development of autism.

    Further information can be found here:

    Science Direct
    Vaccines and Autism
    No Link between Vaccines and Autism
    Vaccines Still Not Linked to Autism
    Vaccines and Autism Fact Sheet