The body's natural defence mechanism against infectious diseases.
A small amount of dead or weakened pathogen is introduced into the body. It prepares the immune system to prevent future infections with the live pathogen.
A micro-organism that causes disease.
A list of often difficult or specialised words with their definitions.
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus
The smallest of living organisms. Viruses are made up of a ball of protein that contains a small amount of the virus DNA. They can only reproduce after they have infected a host cell
A viral infection of the breathing system which attacks the lungs and can be fatal
The human immune system recognises and destroys pathogens inside the body. Pathogens, such as bacteria and viruses, cause damage and disease when they grow and reproduce. Vaccination enables the body to respond more quickly to future infection by that pathogen.
Highly-magnified, digitally-colourised image of the virus H1N1,
sometimes called "swine flu".
Photo courtesy of CDC/Cynthia Goldsmith
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