Vaccines

A vaccine is a material containing weakened or killed Th pathogens and is used to produce immunity to a disease by stimulating the production of antibodies.

In 1796, a British physician, Edward Jenner, infected a young boy with cowpox, by injecting pus cells. After the boy had recovered from cowpax, Jenner injected the pus cells from a smallpox patient into him. The boy did not get smallpox.

So it became clear that intentional infection with cowpox protected people from smallpox. This method i was named "vaccination and the substance used to vaccinate was called a vaccine.

The Mode of Action of Vaccines
Pathogens contain special proteins called

"antigens". When pathogens enter the body (blood) of host, these proteins stimulate the immune response in host i.e. synthesis of "antibodies" Antibodies bind to pathogens and destroy them. In addition, "memory e cells are produced, which remain in blood and tha provide protection against future infections with the same pathogen.