Why do doctor inject the sick with small amounts of dead viruses?

they inject people with small amounts of deadly viruses to get us immune  to it so its harder for the body to get sick. like the flu shot it basically kind of has the flu in it and when you get injected with it the body gets immune to it so its harder for you to get sick with the flu because your bodies already immune to that virus hopefully this helped  

Explanation:

there should be recorded video of the class under the assignments for the day

answer(d) call 911;