How does a vaccine work?

Vaccines train our immune system to specified disease-causing pathogens, without getting sick first, in order to protect against infectious disease in future. 

They contain the same antigen that is found on pathogens that cause the associated disease, but exposure to the antigens in vaccines is controlled. 

Antigens are made by using killed or weakened versions of the disease-causing germ or parts of the germ.

When someone gets a vaccine, their immune system responds to the vaccine the same way as it would be the real germ.

1. It recognizes the germ present in the vaccine as a foreign material.

2. Then it responds to the germs present in the vaccine, by making antibodies, just as it does for the real germ.

3. It remembers the germ and how to defend or destroy it. Now, if the vaccinated person ever exposed to the disease-causing germ in the future, then their immune system will be able to quickly destroy it before it has a chance to make them sick.