why vaccination can works for same group of microbes
Cowpox and smallpox are closely related viruses, and they share antigens (antibody recognition sites) on their outer coat. Cowpox is not nearly as virulent as smallpox – patients infected with it got sick but rarely died.
When exposed to cowpox, the immune system generates antibodies to neutralize it. These antibodies are still present if the patient is later exposed to smallpox. They bind to the smallpox virus, tagging it for clearance and destruction by other components of the immune system.