There are many different types of bacteria and viruses. If you get a virus or bacteria that you have not had before, it can make you ill. Vaccination prevents you from becoming seriously ill, and may prevent you from getting any symptoms. Read more to find out how it works.
Immune system
Pathogens, such as bacteria and viruses, can make you ill. The body’s immune system responds to protect you from that. The immune system is a network of cells and substances that are specifically for fighting pathogens.
It is made up of two parts.
- Some cells fight all pathogens. They respond very quickly, but not very effectively. This part is called the innate immune system, because it works well as soon as a baby is born.
- There are also cells that are very effective at fighting pathogens, but do not know how to do that right away. These cells do not know that the pathogen even exists at first. They need to learn to recognise each pathogen separately – but will remember for a very long time. Possibly even forever. That is why this is called the adaptive immune system.
Acquiring natural defence
Each time the adaptive immune system encounters a new pathogen, it must learn to recognise it. This may take some time, because each cell of the adaptive immune system recognises a very tiny piece of a pathogen. That is why you become ill when you encounter a new pathogen.
Once the cells of the adaptive immune system recognise the pathogen, they get even stronger. Three things happen then:
- The cells multiply rapidly to fight the pathogen more effectively.
- Some of the cells produce antibodies. The antibodies attach to the pathogen, interfering with its ability to function.
- The antibodies also communicate to let other nearby immune cells know that they have found a pathogen. This helps the innate immune system join in and fight the pathogen more effectively.
Immunological memory
Once the pathogen has been destroyed, most cells and antibodies disappear. But a small portion remains. They are like guards, or sentinels. If the same pathogen returns, these antibodies immediately attach to them, so the remaining cells are reactivated.
Since there are a lot more of these cells and they already know what to do, this takes much less time than before. That is why this is called the memory function of the adaptive immune system. The cells immediately start to multiply again to fight the pathogen and produce more antibodies. As a result, you will be much less ill, and may not have any symptoms at all.
Tiny fragments of virus in a vaccine
The body can already do a lot on its own. But becoming ill is not just unpleasant, it can also be dangerous. It is important that the immune system learns to recognise the pathogen without making you ill. That is what a vaccine does.
A vaccine contains tiny fragments of the pathogen, or a few attenuated (weakened) or inactivated pathogens. Since they are weakened, dead, or fragmented, they cannot make you very ill. But the immune system now sees the pathogen and can learn to recognise it.
That means that your immune system can fight the pathogen more effectively next time that you encounter the virus. As a result, you will not become ill at all, or only have mild symptoms.
Side effects and additional vaccine doses
After a vaccination, you may experience side effects, such as a sore arm or fever. These symptoms usually go away after a few days. Sometimes your immune system needs to be reminded several times before it can recognise the pathogen. In that case, you need more than one vaccine dose.
Would you like to know more about the contents of vaccines? Read more on the page ‘What is in vaccines?’.