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9 frequently asked questions about immunisation

Child playing doctor with bearWhen you have a new baby you often find yourself in unfamiliar territory navigating a brand new world full of brand new experiences — nappies, feeding, sleep, teething, the list goes on.

It is important to ask questions and arm yourself with the right information so you can make informed decisions.

When it comes to immunisation, parents have many questions. Here we ask Associate Professor Chris Blyth to answer some of the most frequently asked questions about immunisation.

Dr Blyth is Deputy Chair of the Australian Technical Advisory Group on Immunisation (ATAGI) and a Paediatrician, Infectious Diseases Physician and Clinical Microbiologist at Princess Margaret Hospital for Children, Path West Laboratory and University of Western Australia.

9 frequently asked questions about immunisation

Why should I vaccinate my child?

Vaccination is the safest way to ensure your child is protected against infections that either are common or were once common causes of severe childhood infections.

Vaccinating your child against these infections means that their immune system, the part of the body that protects them against infections, can quickly recognise bacteria or viruses and respond appropriately protecting your child should they be exposed to these germs.

What is ‘herd immunity’?

In addition to preventing infection in vaccinated children, vaccination helps protect unvaccinated members of society.

If the majority of people in society have protection, either through vaccination or natural infection, it is harder for a germ to pass from person to person. It is this passage from person to person that is required for a germ to continue to infect people.

A good example of this is what happens with measles. We rarely see measles in Australia today. If we do, it is normally in an unvaccinated individual who has either travelled to a country where measles is circulating or is exposed to such a person who has acquired measles overseas. Because most people are immune, even when we have a person who develops measles, it is very hard for the virus to find non-immune people and therefore to move from person to person. This is an example of herd immunity – immunisation protects the society or “herd” from ongoing measles transmission.

If we didn’t maintain very high levels of immunity to measles, the virus would spread rapidly through the community and would result in many children and adults developing severe disease including severe lung and brain infections. A significant number of these infections would be fatal.

What is in vaccines? Is there mercury in vaccines?

There are two major components of vaccines. Firstly, vaccines contain antigens. These are small components, such as proteins or sugars, that are derived from the virus or bacteria we are trying to protect against. In some vaccines, a modified germ is used, which resembles the original virus or bacteria. This part of the vaccine is included to mimic the infection, tricking the body into thinking it has been infected.

Many vaccines contain adjuvants. Adjuvants are substances that help promote a more vigorous immune response to the antigen. These promote a stronger and longer-lasting immune response.

Some vaccines used in children used to contain preservatives including a chemical derived from mercury (thiomersal). Although no link between thiomersal and side effects was ever demonstrated, thiomersal is no longer used in vaccines recommended for Australian children.

Is it true that some people can still catch a disease even after vaccination?

No immunity is 100%, even the protection that occurs after you are exposed to natural infection. A small proportion of the population will not generate immunity after exposure to an infection or vaccine. Immunity against some infections also wanes over time and may need to be boosted.

Despite this, the number of vaccinated children who develop disease after exposure is many times lower than unvaccinated children. For a number of diseases, infection is also less severe in vaccinated children compared with unvaccinated children.

Will all these vaccines at once overload a baby’s system?

Immunity is something that develops over a child’s life. A child is born with a very naïve immune system. A child is exposed to many new antigens everyday: exposure to things in the environment including specific germs enables a child’s immune system to learn.

The vaccines used today only contain the necessary components to induce an immune response. Vaccines form only a small part of the total number of the new antigens that a child is exposed to each day.

The vaccines included on the schedule are those offering protection against diseases most common or most deadly at certain ages. This is why we include a number of vaccines in the first year of life, a time when the child is most vulnerable.

Sometimes, immunity needs to be boosted, by “re-exposing” a child’s immune system to a vaccine to “remind” it.

Is it OK to space out my child’s vaccinations?

To provide the best protection for your child and the community, it is recommended that children receive all vaccines offered free on the National Immunisation Program at the time points recommended.

For children with specific risk factors for more severe disease, modified schedules are sometimes recommended. Modifying the schedule (i.e. by spacing it out) means that children are susceptible to infections for longer periods of time.

Also, if parents chose to receive only one vaccine per visit, a child will require more immunisation visits.

What are the side-effects?

Vaccination exposes a child’s immune system to something new, something that the immune system needs to recognise as foreign or different in order for it to develop targeted protection. It is therefore not uncommon that your child will develop a mild reaction to the vaccine. The most common side effects are low-grade fever or pain or redness at the injection site.

More severe side effects are uncommon following vaccination. The type of reaction varies depending on the type of vaccine used. Uncommon events such as severe allergy (e.g. anaphylaxis), febrile convulsions and intussusception (a bowel problem in young children) occur in a very small number of children following routine vaccination. The rate of these uncommon events following vaccination is usually hundreds to thousands of times less frequent than complications that can develop following the infection that each vaccine is trying to prevent.

If a child does develop more severe side effects following vaccination, it is important to seek advice from a health care or immunisation provider. A reaction that occurs following immunisation may be related to the vaccine but also may have occurred regardless of vaccination. Uncommon or severe adverse events need to be considered when managing a child’s future vaccination. Documenting these is also essential to Australia’s vaccine safety monitoring.

Is there a link between vaccination and autism?

Autism is a developmental condition, whose first clinical signs commonly occur in the 2nd year of life. As this is a time when vaccinations are frequently given, many have questioned whether there is a link. Any link between vaccination and autism has been disproven in a number of well-conducted studies which have shown the rate of autism is as frequent in vaccinated and unvaccinated children. The report that initially raised this possibility was shown to have been fraudulent and was retracted by the medical journal that published it.

Is there a link between vaccinations and allergy/asthma?

The rate of allergy and asthma has increased in the last few decades, the cause of which remains unknown. Similar to autism, many have questioned whether increasing use of vaccination is influencing this, yet studies have shown similar rates of asthma and allergy in vaccinated and unvaccinated children.


This blog post is sponsored by the Australian Government Department of Health

The Australian Government’s ‘Get the facts about immunisation’ campaign has been developed to give you the facts about immunisation so that you can make informed decisions in the best interests of your child and our community. Click here to get the facts about immunisation.

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1 Comment so far -
  • Belle says:

    Oooh yes, vaccines are great! I’d advise you all to do your own research on this one, which may include watching documentaries such as Vaxxed, The Greater Good and The Truth about Vaccines. The body is born perfect and given the right nutrition etc. the body certainly does not need unnecessary chemicals being injected into the bloodstream.

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