While we think of vaccines as relatively modern, the concept of using modified infectious agents to "protect" us has been in practice for thousands of years.

Two thousand years ago, records from China and India describe inoculating people with scabs from others with mild cases of small pox. This was risky and many died but the practice persisted.

Then came Edward Jenner, an English physician who in 1796 established that people were protected from smallpox when they were inoculated with cowpox, a related virus generally not a threat to humans. Thus, Jenner coined the word vaccination which is derived from the Latin — vacca for cow.

This use of a related, less virulent or non-disease causing microbe to cross- protect people was a huge step forward. It's the concept on which many vaccines continue to be produced.

Louis Pasteur, considered the father of microbiology, discovered the concept of using a weakened or attenuated form of a microbe to produce immunity. In a popular story, an assistant left cholera bacteria in the lab while he went on holiday.

When he returned, they injected the bacteria in chickens but the birds did not die. The bacteria had not only lost its lethality but created an immunity that protected the chickens from subsequent cholera infection.

Pasteur is perhaps most recognized for the rabies vaccine he developed in 1885. He used dried spinal cord material from infected rabbits. The process of drying inactivates the rabies virus so that when it is injected into people, they produce antibodies and other elements of immunity.

Today we have an incredible list of vaccines that protect us from fatal and crippling diseases. Yet we have a long way to go.

We desperately need vaccines for HIV, tuberculosis and even for chronic diseases like Alzheimer's and Parkinson's.