You are presented with the question "What leads to immunity and extremely rarely with serious side effects?" and the following answer choices: 
- hydration
 - peachleaf willow
 - homeopathy
 - veterinarians
 - vaccination
 - Allergies
 - exposure
 - Chemical energy

Now knowing that immunity results from immunization and serious side effects resulting from vaccination are extremely rare, choose the best answer.


 

     vaccination    