Answer: The vomiting phase will usually only last from 1-3 days but the diarrhea may continue for 1-2 weeks.
When you or your child starts throwing up, one of the first things that cross your mind is, "Oh my gosh, when will this be over?" The duration of illness caused by stomach / intestinal viruses varies by the particular virus and from person to person. Usually the vomiting phase only lasts for part of 1 day. A typical scenario is that the child wakes up at 2am and vomits every 30 minutes for 5 hours. Then they go to sleep. When they wake up, they can usually hold down a sip or two of liquid. They refuse to eat much for a few days but are drinking. If your child can not hold liquid down when they wake up after that initial night of vomiting, you need to see a doctor about some anti-vomiting medication. When they start to eat a little more food, a few children may have a relapse and vomit again. We call this the "last hurrah" and it is usually just happens one time 2-4 days after you thought they were done vomiting. After that "last hurrah", the child starts to get better. The diarrhea can easily last for 10 days. Occasionally they have a relapse and vomit one more time a week later.
Stomach bugs are different for everyone, though. A stomach bug came into my home in February 2014. My 6 year old daughter woke up one Saturday with a bad tummy ache and a fever of 100.5. She stayed in bed ALL DAY. Drank a little water but ate nothing. The next day she still had a tummy ache. She vomited a tiny bit ONE TIME. She stayed in bed all day Sunday. On Monday, she felt better and got up to play, but she didn't eat anything until Wednesday. There were 4 days that she ate almost nothing but she was drinking. She never had diarrhea. My 3 year old son somehow managed to catch it from her. He got sick that Thursday night and vomited 10 times. He was so much sicker than my daughter. He had diarrhea for a week. He had a relapse of vomiting 22 hours after I thought he was done and then again 3.5 days later!
The last 2 stomach bugs that I have had, only lasted 1 day for me (24 hours). I vomited 2-3 times in the evening, rested and didn't eat much the next day, and was fine the day after that. I never had diarrhea. However, my 18 month old son had the same virus, he vomited off and on for 48 hours and then had diarrhea for 10 days. My 6 year old niece had a terrible stomach bug in December 2012. She vomited off and on for over 3 days. She couldn't keep anything down (not a sip of water or ice or anything) for 3 full days. Finally, my sister took her to the ER where they gave her a Zofran tablet that melted in her mouth. She ate a popsicle 30 minutes later with no problem. If you have been vomiting more than 12 hours, I would get to the doctor or ER for a prescription of an anti-vomiting medication (Zofran or Phenergan) and stop your suffering. Please be aware that you will still be contagious for at least 3 days after you are well and your symptoms have stopped.
Please consult your physician if your illness is severe or if it continues too long.
--Annie Pryor, Ph.D