Do you mean the "stomach flu".

Seasonal Flu vs. Stomach Flu - What is the Stomach Flu

Try pedialyte if he can keep that down. It's full of electrolytes. Even a sip here and there will do wonders. Don't have him try to guzzle a bunch, it will just come back up. Seriously, try a teaspoon at a time.

Also, there's a medication called Emetrol that is for nausea. It's over the counter.

Keep an eye on his urine output. Also, increased heart rate, weak pulses, deep breathing, and cool, mottled extremities are a sign of severe dehydration.

Hope he feels better!