It can be contagious from a few days up to two weeks or more, depending on which virus is causing your stomach flu (gastroenteritis). A number of viruses can cause gastroenteritis, including noroviruses and rotaviruses.
The flu shot protects against influenza, which isn't the same thing as the stomach flu (gastroenteritis). Gastroenteritis is an infection caused by a variety of viruses, including rotaviruses and noroviruses. Although it is often called the stomach flu, gastroenteritis is not caused by influenza viruses. Influenza attacks your respiratory system — your nose, throat and lungs. Yes it is highly contagious: Noroviruses (the kind that cause stomach flu) are very contagious and can spread easily from person to person. Both stool and vomit are infectious. Particular care should be taken with young children in diapers who may have diarrhea. Some people may be contagious for as lon … g as 2 weeks after recovery.  (From the CDC website-CDC.gov) The viruses that cause the stomach flu (viral gastroenteritis) are present in the feces and vomit of the sick person. Illness is spread when a few of these viruses accidentally get into someone else's mouth. The stomach flu is highly contagious and is primarily spread through the fecal-oral route. Technically, you need to swallow the virus to get the illness. When a person has viral gastroenteritis, the viruses are present in their feces and vomit.  You can be contagious from a few days up to two weeks or more, depending on which virus is causing your stomach flu (gastroenteritis). A number of viruses can cause gastroenteritis, including noroviruses and rotaviruses. The contagious period — the time during which a sick person can give the illness to others — is slightly different for each virus. 1  Norovirus. 2  With norovirus — the most common cause of viral gastroenteritis in adults and children — you're contagious from the moment you begin to feel ill Transmission of Stomach Flu. Depending on the type of virus, stomach flu can be very contagious and spread quickly from person to person. Once a person is exposed to the virus, the symptoms usually appear within 4 to 48 hours and last for 1 to 2 days. Treating Viral Gastroenteritis. Due to the stomach flu being caused by a virus, antibiotics will not work at all. However, due to the dehydration caused by the vomiting and diarrhea, the best treatment is to intake lots of fluid. View larger image. Norovirus is a highly contagious virus. Anyone can get infected with norovirus and get sick. Also, you can get norovirus illness many times in your life. One reason for this is that there are many different types of noroviruses.  351,758 Helpful Votes. 386 Followers. A. While it's commonly called the stomach flu, viral gastroenteritis has nothing to do with the actual flu. Cramps, diarrhea, and vomiting are the hallmarks of highly contagious gastroenteritis, which gains notoriety when it tears through cruise ships, conventions, etc.  Stomach flu or gastroenteritis is a general term for a number of inflammatory problems that occur in the gastrointestinal tract. Gastroenteritis is a better term because when some individuals use the term stomach flu , they get the term confused with the flu (influenza) and the viruses that cause the flu. Influenza viruses do not cause stomach flu. Gastroenteritis most commonly causes symptoms of. 1  diarrhea, 2  nausea, 3  vomiting and. 4  abdominal pain. Unfortunately, there are many causes of stomach flu. The most common causes are contagious gastroenteritis are. 1  viruses (for example, Norovirus, Adenovirus and others), 2  bacteria (for example, Salmonella, Shigella, E. coli and others), and. 3  parasites (for example Giardia lambia, Cryptosporidium, and others). Stomach flu is an intestinal infection caused by several different viruses that can result in diarrhea and vomiting. A highly contagious condition, the stomach flu is the second most common illness in the United States. It causes millions of cases of diarrhea each year. 
http://www.mayoclinic.org/diseases-conditions/viral-gastroenteritis/expert-answers/flu-shot/FAQ-20058565 http://www.answers.com/Q/Is_the_stomach_flu_contagious http://www.stopthestomachflu.com/Home/how-is-the-stomach-flu-transmitted http://www.mayoclinic.org/diseases-conditions/viral-gastroenteritis/expert-answers/stomach-flu/faq-20057899 http://www.buzzle.com/articles/is-stomach-flu-contagious.html http://www.cdc.gov/norovirus/about/transmission.html http://answers.webmd.com/answers/1197786/is-stomach-flu-contagious http://www.medicinenet.com/is_the_stomach_flu_gastroenteritis_contagious/article.htm http://diarrhea.emedtv.com/stomach-flu/stomach-flu.html
how contagious is a stomach flu