Norovirus causes sudden, intense vomiting and watery diarrhea that typically hit 12 to 48 hours after exposure. Most people recover fully within one to three days, but the illness can feel severe while it lasts. Here’s what to expect and what to watch for.
The Main Symptoms
The hallmark of norovirus is how fast it strikes. You can feel perfectly fine one moment and be doubled over with nausea the next. The core symptoms are vomiting, watery or loose diarrhea, and stomach pain. Vomiting tends to be more prominent with norovirus than with many other causes of stomach illness, and it often comes in waves rather than as a single episode.
Beyond the gut symptoms, many people also experience low-grade fever, headache, muscle aches, and general fatigue. These systemic symptoms are usually mild compared to the vomiting and diarrhea, but they add to the overall misery. Chills are common too, especially during the first 24 hours.
How Quickly Symptoms Appear and How Long They Last
The incubation period is 12 to 48 hours. That means you won’t feel sick right away after picking up the virus. Most people notice the first wave of nausea roughly a day after exposure, though it can come as early as 12 hours.
Once symptoms start, the worst is usually over within one to three days. The first 24 hours tend to be the most intense, with frequent vomiting and diarrhea. By day two or three, episodes taper off and appetite slowly returns. Even after you feel better, though, the virus continues to shed in your stool for days, which means you can still spread it to others. Careful hand-washing during this window matters.
Dehydration: The Real Risk
Norovirus itself isn’t dangerous for most healthy adults. The real concern is dehydration from losing so much fluid through vomiting and diarrhea. Young children, older adults, and people with weakened immune systems are especially vulnerable because they have less fluid reserve and may not be able to drink enough to keep up with losses.
Signs of dehydration to watch for include:
- Excessive thirst and dry mouth
- Dark-colored urine or urinating much less than usual
- Dizziness or lightheadedness when standing up
- Weakness or unusual fatigue
In infants and toddlers, look for fewer wet diapers, no tears when crying, and unusual fussiness or sleepiness. Small, frequent sips of water or an oral rehydration solution work better than trying to drink large amounts at once, which can trigger more vomiting.
How Norovirus Feels Different From Food Poisoning
Because the symptoms overlap so much, it’s easy to confuse norovirus with food poisoning. The timing is your best clue. Food poisoning from bacteria typically hits within a few hours of eating contaminated food, while norovirus takes one to two days to show up. Norovirus also tends to involve more nausea and vomiting relative to diarrhea, whereas bacterial food poisoning often leans the other way, with more diarrhea (sometimes bloody) and severe abdominal cramping.
The seasonal flu is a different illness entirely. Influenza attacks your nose, throat, and lungs, causing cough, congestion, and respiratory symptoms. Norovirus targets your stomach and intestines. Despite the nickname “stomach flu,” norovirus has nothing to do with the influenza virus.
Not Everyone Gets Sick
Interestingly, not everyone who catches norovirus develops symptoms. A large meta-analysis published in The Lancet estimated that about 7% of people carrying the virus at any given time are completely asymptomatic. During outbreaks, that number climbs to around 18%, meaning nearly one in five infected people feels fine but can still spread the virus. This is one reason norovirus tears through households, cruise ships, and schools so efficiently: people who don’t know they’re infected keep passing it along.
Warning Signs That Need Medical Attention
Most norovirus infections resolve on their own. But certain symptoms suggest something more serious is going on, either severe dehydration or a different condition altogether. Seek medical care if you notice vomit that contains blood, looks like coffee grounds, or is green. Rectal bleeding, severe abdominal pain, or a high fever with a stiff neck also warrant prompt evaluation. Signs of significant dehydration, particularly dark urine, dizziness on standing, and extreme weakness, mean your body needs more fluid than you’re able to take in by mouth.
For young children and older adults, the threshold should be lower. If a child can’t keep any fluids down for more than a few hours, or if an elderly person becomes confused or unusually lethargic, those are signals to get help sooner rather than later.