I give my son a shot anytime he vomits now. He vomited one time about 4 mos ago (he is 3 years old CAH salt wasting) and he seemed fine, ate a bit, and did not vomit again. I put him to bed w/ no worries. I went to wake him up at 8:00 am and could not wake him. He was very sweaty, soaked! I got him to drink some juice, but he was very limp etc...we gave him the shot and then called endo, he said take him to the pedatrician if he doesnt improve, he did improve, I took him anyway just to check him over, they said he got low blood sugar. So I give the shot no matter if he only vomits once and give him lots of sweet juice!