Vaccines were developed out of the germ theory of disease.
The germ theory of disease is the idea that microorganisms are the cause of many diseases. Although it had been proposed a number of times in history, it wasn't until the mid nineteenth century that the scientific work of Louis Pasteur and others proved that microorganisms cause most infectious diseases. Pasteur and other scientists used this information to develop safe vaccines to help people develop immunity to certain diseases before ever contracting them.
The germ theory of disease
eventually led to the development of certain types of vaccines. This theory explains
that specific type or types of microorganisms, which are bacteria, virus, fungi,
or protest species, cause some diseases. These organisms can enter the human
body, and can even grow and reproduce, causing infection, inflammation to
specific organs in the body, and others. One particular vaccine developed successfully
through this understanding is the smallpox vaccine, which is an important
vaccine up to this day.
