Fact 1: Immunity results from immunization.

Fact 2: Serious side effects resulting from vaccination are extremely rare.

Given the two facts above, answer the question "What leads to immunity and extremely rarely with serious side effects?" with the following options: 
- hydration
 - peachleaf willow
 - homeopathy
 - veterinarians
 - vaccination
 - Allergies
 - exposure
 - Chemical energy


 

     vaccination    