The flu does not turn into strep throat. However, it is possible to get strep throat after being sick with the flu. You can also contract the flu after being sick with strep throat. Despite this, the flu does not “turn into” strep throat, and strep throat does not turn into the flu.
Flu shots work by taking advantage of the body's natural defense system: the immune system. When the vaccine enters the bloodstream, it releases viruses into the blood…If the flu later appears (in an active form), the immune system will recognize it from the vaccine and be able to provide antibody protection. This is how the flu shot works.