A microorganism is bacteria, viruses and fungi. The ones that cause dieases are called pathogens. Pathogens produce toxins. Toxins are poisons and they cause damage to the body. Viruses will infect the body cell. Get inside it and then start to reproduce itself. Eventually the cell will break open and it will be permanently damaged.
White Blood Cells
The body defends against pathogens using white blood cells. These are cells found within the blood of the body. They have 3 ways of defending the body:
They can ingest pathogens
They can produce antibodies
They can produce antitoxins
A white blood cell will recognise the pathogen. It will then move towards it and surrond it. Then the white blood cell will engulf the pathogen. When the white blood cell has fully engulfed the pathogen it will release enzymes. Enzymes are chemicals that are able to break down and digest the pathogen. The pathogen will then disappear and will become harmless.
The white blood cell will produce many different antibodies.
Then the antibodies will attach to the antigens on the pathogens.
Then the antibodies will start destroying the bacteria.
The white blood cells produce antitoxins. Antitoxins make the toxins harmless.
In a vaccine is a dead or inactive form of a pathogen. This means that it won't harm the body in any way. On the surface of the dead pathogens body it still has the antigens. This means that the white blood cells learn to make the correct antibodies for that type of pathogen. This means that the body won't get this disease because the white blood cells have memorised how to produce the antibodies.
If more people in a population are vaccinated then it becomes harder for the disease to spread.
The MMR vaccination is against measles, mumps and rubella.
Some scientists think that it is linked to autism.