Question

What specifically do vaccines contain which cause your body to become

Answer 1

Answer:

I'm not entirely sure, but I've heard that vaccines contain very weak amounts of the virus in order to expose your body to it, so that your body can become immune to it before being exposed to the real thing.

So basically, a flu shot contains a weak version of influenza.

I don't know this for sure, but hopefully this helps!

Answer 2

Certain molecules from the pathogen must be introduced into the body to trigger an immune response. These molecules are called antigens, and they are present on all viruses and bacteria.