Substances added to vaccines to strengthen the body's protective immune response to the vaccine.

Adverse event

Any kind of symptom or health event experienced after vaccination. Not all adverse events are caused by the vaccination; some may be coincidental.


A severe allergic reaction of sudden onset and rapid progression, usually accompanied by hives and/or flushing of the skin. It affects two or more organ systems at once and can lead to difficulty breathing, feeling dizzy and/or abdominal pain with vomiting.5


Proteins made by cells of the immune system that can identify microorganisms like bacteria and viruses and prevent them from infecting cells.


The parts of pathogens or their toxins that are used in vaccines to provoke an immune response.


Single celled organisms (living things) that exist in our body and our environment. Most bacteria are harmless and some are beneficial to humans; however, some bacteria can cause disease.

Herd immunity

Occurs when a significant proportion of individuals within a population are protected against a disease through immunisation. This offers indirect protection for people who are still susceptible to the disease, by making it less likely that they will come into contact with someone who is carrying the pathogen. Find out more about herd immunity


The process through which people are protected against illness caused by infection with pathogens.


The state of protection that occurs when a person has been vaccinated or has had an infection and recovered. Vaccination, like infection, confers immunity by activating the immune system.

Infectious disease

A disease acquired from another human, or sometimes from animals. When an infectious disease is acquired, it means the pathogen has entered the body and started to multiply causing damage to tissues in the body.


A process that occurs when the immune system identifies something foreign in the body. This can appear as redness, swelling and pain. Inflammation may occur at the injection site after a vaccine, because this is a normal and expected response that shows the vaccine is being effective.


Very small living things, including bacteria, viruses, and parasites. Microorganisms that cause disease are called pathogens.


Any kind of infectious organism that causes disease.


The substance used for immunisation. Vaccination refers to the act of giving a vaccine to a person.


A tiny infectious agent that needs cells from other organisms to survive and multiply.


© 2021 Australian Academy of Science