Your Body’s Secret Superpower: The Immune System and Immunisation

If you ever wished you had a superpower – especially in the face of multiple exploding nappies or that sinister silence that means a toddler is up to no good – you’ll love to hear that your body already has one. It’s called your immune system and it’s an invisible forcefield that protects you against potentially harmful organisms.

Let us at the Immunisation Advisory Centre explain how your, and your little one’s, immune system works and how immunisation supports it.

What is the immune system?

The environment around us is full of a wide range of potentially harmful organisms (also called pathogens), like bacteria, viruses, fungi and parasites, which cause disease if they enter our bodies and multiply.

The human body is pretty clever in responding to the threat these pathogens present. It has various defence mechanisms to physically prevent them from entering our bodies, or, if they do get in, to kill them.

One of our body’s most important defence mechanisms to identify and destroy an invading pathogen is the immune system. Immunisation supports the immune system, helping our bodies to respond more quickly to an attack and preventing disease.

Each invading pathogen has unique parts, called antigens. These allow the immune system to tell the difference between ‘self’ (our bodies) and ‘non-self’ (the pathogen).

The first time the immune system sees a new antigen, it prepares to destroy it. During this time, the pathogen can multiply and cause disease. But, if the same antigen is seen again, the immune system is now ready to confine and destroy it quickly. This is called adaptive immunity.

How does immunisation help boost our bodies’ defences?

Vaccines use this adaptive immunity to expose our bodies to the antigen without causing disease. This means when the pathogen infects our bodies, the immune system response kicks in quickly and the pathogen is stopped from causing disease.

The immune system in action

When the immune system is alerted that something foreign has entered our bodies, an immune response is triggered.

The immune system swings into action: white blood cells destroy the infection or take chemical messages to other parts of the immune system. It remains on the lookout for potential sources of attack or abnormal cells.

Antigens and antibodies

We mentioned above that invading pathogens have unique parts, called antigens. When faced with invading pathogens, our immune system responds by producing antibodies that bind to antigens.

These antibodies have a range of functions, including acting as flags to direct the immune system to foreign material. Although on a normal day, low levels of antibodies circulate in our bodies, when an immune response is activated, greater amounts are produced to specifically target the foreign material.

Vaccination increases the levels of antibodies against a certain antigen. 

Our bodies’ primary response

If our bodies are exposed to an invading pathogen, it’ll attempt to isolate and destroy it by producing antigen-specific antibodies. When our bodies are first exposed to an antigen, several days pass before this response becomes active which means it can’t prevent disease, but it can help you recover.

The really clever bit here is that following an infection, some memory cells remain – this means our bodies and immune systems remember specific antigens and how to attack them. This memory can take a few months to fully develop.

Our bodies’ secondary response

If our bodies are exposed again to the same pathogen, our immune system can respond quickly. These secondary immune responses can usually prevent disease, because the pathogen is detected, attacked and destroyed before symptoms appear.

As an adult, you’ll probably respond more quickly to infection than your child. That’s because secondary immune responses mount a quick and strong immune response to antigens they’ve previously experienced. Because children haven’t had as much exposure to antigens, they’re more likely to get sick.

Memory of the infection lingers in our bodies, with long-lived antibodies hanging around. Some infections, like chickenpox, induce a life-long memory of infection. Others, like influenza, vary from season to season to such an extent that even us adults can’t adapt.

Vaccination takes advantage of this secondary response. It exposes our bodies to antigens and activates the immune system without causing disease.

The initial response to a vaccine is like when our bodies are first exposed to a pathogen: slow and limited. But subsequent doses of the vaccine boost this response, resulting in the production of long-lived antibodies and memory cells, just like what would happen naturally following subsequent infections.

The aim of vaccines is to prime our bodies, so that when we’re exposed to disease-causing pathogens, our immune systems can respond rapidly and at a high activity level. This destroys the pathogen before it causes disease and reduces the risk of it spreading to other people.

To be fully immunised, for most vaccines, you may need more than one dose to provide long-lasting protection.

For a more in-depth look at the biology behind this, visit our immune system and immunisation page.