evidence: Learn more: How Flu Spreads [...] CR: Flu vaccines work by giving your body a little peek at the proteins, or the composition of the virus, and stimulate your body to make defenses against that recipe, if you will. That way, when you encounter the influenza virus in the wild, your body is already revved up and familiar and is able to really combat that virus. [...] JS: No, you cannot get the flu from a flu shot. And that is because flu shots don't actually contain live flu virus.