Why do some people get the stomach flu and others dont?

Just wondering if there's some scientific reason as to why it's so hit or miss.

No such thing as the stomach flu? What is it called then when you have diarrhea/vomiting? Isn't that contagious?

The correct term is "Gastroenteritis." Stomach flu is a more common layman's term that is loosely used for the public.

It is, however, hit and miss. Families who share closed quarters, drink after each other, etc., may be more likely to see a spread between them, than casual contact. Such as if you're seated next to someone who has a "cold," this doesn't necessarily guarantee that you'll get one too, but you might.

It's just the nature of viral transmission.

Hygiene counts for a lot. The virus that causes "stomach flu" is called norovirus. It is contracted via ingestion of particles. Brace yourself, it's gross. These particles are shed in the feces and vomit of infected people. When these people have violent episodes of either in the bathroom (or wherever they are -- you hope it's a bathroom), the vomit and diarrhea can splatter and aerosolize into the environment. The next person that walks in can accidentally ingest these microscopic particles and pick up norovirus.

The way to limit transmission is to enforce thorough and frequent handwashing after using the bathroom, after changing diapers, and while preparing food. Also, don't bite your nails or stick your fingers in your mouth. And definitely don't let people sick with noro handle any food.

If someone throws up or has a diarrheal episode in your bathroom, carefully clean up the place with a dilution of bleach. Noro is very hardy and survives in the environment for a while. And of course, keep washing your hands.

No such thing as stomach flu.
Flu is a virus that affects muscles and joints, and we are all susceptible to catch it, just that some peoples immune system is better than others.