Immunizations for Kids – how immunizations work

This page gives information about how the immune system works and how immunizations for kids provide protection from infectious diseases.

To read more on the diseases immunizations for kids protect against, click here.

To read about the childhood immunization schedule for your country, click here.


What is a vaccine?

A vaccine is an agent that stimulates the body's immune system to provide a response that will mean protection from that disease in future. So whooping cough vaccine leads to immunity from whooping cough.

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What is an immunization?

An immunization refers to the process when the body develops immunity to a vaccine. Sometimes, vaccine and immunization are used interchangeably, so immunizations for kids and vaccines for kids mean the same.

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How does the body defend itself against disease?

There are many mechanisms the body uses as defence, including :

  • the skin – it is a barrier to many bugs
  • mucus – bugs get caught up in it and coughed out
  • nose hairs – these stop bugs getting in
  • "good" bacteria – we have bacteria in our gut that help protect against disease. These "good" bacteria are present in probiotics
  • lysosyme in tears – this is an enzyme that breaks down bacteria
  • acid in the stomach – acid kills loads of germs that get to the stomach
  • fever – bugs are uncomfortable being hot as well as us. Fever is a protective mechanism the body has. Read more
  • the immune system – this is how immunizations for kids work and there is more about this below

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How does the immune system work?

The immune system is a network of cells and organs that protect against disease. Viruses and bacteria that cause disease have antigens on their surface. Antigens are like markers and the body recognises antigens as foreign and fights them.

The white cells in the blood are one of the main arms in the immune system that fight infections. Some fight the infection by engulfing and ingesting the offending organism, (this is called phagocytosis). Phagocytes that attack the offending organism where they find it are called polymorphs – these usually offer an immediate but a short-lived response.

Other phagocytes called macrophages see the antigen and engulf the cells and then they transport the cells in the lymphatic system to the lymph nodes where they break them down. The lymph nodes are usually enlarged during infections as a result of this white blood cell activity. To read more on large lymph glands, click here.

Other important white cells involved in immunity are the B-lymphocytes and T-lymphocytes. These swing into action after the macrophages have brought the antigen to the lymph nodes, so these cells are not available immediately to fight new infection.

T cells (or T lymphocytes) use chemicals to destroy the cells in your body that are already infected. They also send chemical messages to the B cells to help in their fight against disease. It can take about a week to 10 days for this system to start working for a new antigen, so it is not good as an immediate defence.

B cells (or B lymphocytes) make antibodies. Each antibody is specific for a type of antigen – they join together a bit like a lock and key. If the body has not seen the disease already, it takes time for the antibodies to develop (up to 10 days). Antibodies attach to the antigen and attack the foreign organism both directly and indirectly by alerting other parts of the immune system to the foreign antigen. The B cells also make memory cells which remember that organism so are ready next time to quickly make antibodies.

Immunizations for kids work by making memory B cells. So if you child gets an infection, the body already has experience and can act immediately, rather than waiting for the antibodies to develop from new (which can take up to 10 days by which time the bug will have affected the body). The vaccines used in childhood immunizations mimic the diseases they protect against and the body reacts by making antibodies and memory cells. If your child then gets the infections, the memory cells recognize the antigen and immediately make antibodies which get rid of the organism before it can cause infection – thereby providing protection against that disease. Even if you do get the disease after immunization, it will only be a mild form of the disease. So immunizations for kids are great at boosting natural immunity and protecting your child.

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Why doesn't my child get sick with the immunizations?

Immunizations for kids usually don't make them sick because the part of the bacteria or virus that makes people ill has been removed, killed or changed in some way.

There are various types of vaccines used in immunizations, including:

  • live vaccines – these have been modified to remove the part of the vaccine that causes illness, but they do have the antigen which is a specific marker for that disease, so the body makes the specific antibody.
  • inactivated vaccines - these are made from killed viruses or bacteria, so they have antigen for the body to recognize but they are not dangerous in themselves
  • subunit vaccines – these are made of fragments (eg. Protein, toxoid or polysaccharide) of the organism which the body can recognize and make antibodies against, but the organism is not complete so can't cause disease

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What is the difference between active and passive immunity?

Active immunity is what you get when you a disease or you have an immunization – so the body makes memory cells for that disease. This usually lasts forever, but may wane slightly which is why booster doses of immunizations are sometimes required. This is the basis for immunization for kids

Passive immunity is when you get antibodies to a disease from someone else – this happens when a baby receives antibodies from his mother via the placenta. These antibodies are present only transiently so only provide short term protection. Similar passive immunity is achieved with immunoglobulin treatment.

Immunization for kids provides active immunity.

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  • Vaccination Training Manual. IMAC. 8th edition.

To go to the top of the Immunizations for Kids page, click here

To go to the Infant Immunization Schedule page, click here

To read about immunization side effects, click here

To go to the main Immunization page, click here

To read about swollen lymph glands, click here

To go to the Infections page, click here

To return Home, click here

Last reviewed 22 May 2011

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Dr Maud MD

Dr Maud MD (MBChB, FRACP, FRCPCH), a specialist pediatrician, provides health information and medical advice for parents of babies and toddlers. Read more about Dr Maud.

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