It starts without warning. One minute you are fine, the next you are on the bathroom floor wondering what you ate. Almost everyone blames the last meal. Usually the last meal is innocent, and the clock is the thing that tells you so. Norovirus season runs from October through to spring, and recent seasons have started earlier than they used to, so this is the month to know the difference.
For most of the last decade norovirus outbreaks were dominated by a strain called GII.4, which much of the population had partial immunity to. That changed. GII.17 rose from under a tenth of outbreaks to roughly three quarters of US outbreaks in the 2024 to 2025 season, and it has kept circulating since. Most people have never met it, which is why it moves through households, nurseries and schools so efficiently.
Season start has also crept forward. The 2025 to 2026 season began spiking in mid October, well ahead of the historical pattern, although the total number of outbreaks across that season landed in the normal range. There is still no licensed norovirus vaccine for general use, so prevention is behaviour, not a jab.
Food poisoning from a preformed toxin hits fast. Staphylococcus aureus or Bacillus cereus in food left out too long can make you violently sick within one to six hours of eating. Reheated rice, a buffet that sat out, cream filled pastries. Sudden vomiting, cramps, and it is usually over within a day.
Norovirus takes its time. Twelve to forty eight hours between exposure and symptoms. So the meal you are blaming was probably two meals ago, and the actual source may not have been food at all. It could have been a door handle, a shared bathroom, or a sick child.
Bacterial food poisoning from salmonella, campylobacter or E. coli is slower still. Usually one to three days, often longer, and diarrhoea rather than vomiting dominates. Fever is more common, and blood in the stool points firmly here rather than at norovirus.
Vomiting that arrives with no warning, watery diarrhoea, stomach cramps, and often a low grade fever, aching and headache. It is frequently called the winter vomiting bug for a reason: vomiting leads in adults, while in children diarrhoea is more often the main feature.
It is also short. Most people are through the worst in twelve to sixty hours and functional in one to three days. If you are into day four and no better, that is a reason to get advice, because it is less likely to be norovirus.
One naming problem worth clearing up: the stomach flu is not flu. Influenza is a respiratory virus. They are unrelated, and the flu vaccine does nothing for this.
Alcohol gel works by dissolving the fatty envelope around viruses like flu and COVID. Norovirus has no envelope. It is a hard shelled virus that alcohol largely leaves intact, which is why outbreaks sail through places with hand gel at every door.
What does work:
You are most infectious while you are symptomatic and for the first forty eight hours after symptoms stop. That is the standard advice for staying away from work, school and especially from kitchens and care settings. Virus can continue to be shed in stool for two weeks or more, which is why hand washing stays important long after you feel fine.
The illness itself is rarely dangerous in healthy adults. Dehydration is the thing that puts people in hospital, and it is almost entirely preventable.
Watch for the signs that fluid is losing the race: very little urine or dark urine, dizziness on standing, a dry mouth, sunken eyes, unusual drowsiness, or in a baby, fewer wet nappies and no tears when crying.
If you are unsure whether what you have is a two day inconvenience or something that needs a clinician, a structured symptom check will ask about timing, exposures and warning signs in the order a doctor would, and running it takes less effort than guessing at three in the morning.
The gap between the meal and the misery is the most useful thing you know. One to six hours points at a toxin in food. Twelve to forty eight hours points at norovirus, and at the last person you shared a bathroom with. Stay off for forty eight hours after symptoms stop, use soap and bleach rather than hand gel, and treat dehydration as the real risk.
This article is for general education and is not a substitute for professional medical advice. Seek care promptly for severe dehydration, blood in stool, or symptoms in infants, older adults or anyone who is immunosuppressed.
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