Is the stomach flu the same as seasonal influenza?

No. Seasonal influenza is a highly contagious respiratory illness characterized by fever, body aches, cough as the primary symptoms. Stomach flu, sometimes known as gastroenteritis, is diarrhea and vomiting. The flu shot will not protect you from stomach flu, but will reduce the liklihood of you catching influenza or reduce its severity. Great question! this is a common misconception.
No. Usually the seasonal influenza refers to respiratory infection or lung infection while stomach flu refers to virus that specializes in the gastrointestinal tract that usually leads to diarrhea or nausea or vomiting.