Norovirus is a highly contagious virus that causes sudden-onset vomiting and diarrhea, responsible for 19 to 21 million illnesses in the United States every year. It’s the leading cause of foodborne illness outbreaks and spreads with remarkable efficiency: as few as 18 viral particles can trigger an infection, a number so small it’s essentially invisible.
How Norovirus Makes You Sick
Norovirus is a small, non-enveloped virus with a single strand of RNA as its genetic material. It belongs to the Caliciviridae family, and its particles measure just 27 to 40 nanometers across. That tiny size and lack of an outer fatty envelope are important details, because they make the virus unusually tough. It can survive on countertops, doorknobs, and fabrics for days or even weeks, and it resists many common cleaning products.
Once swallowed, the virus targets cells lining the small intestine. It hijacks those cells to replicate itself, triggering inflammation that disrupts your gut’s ability to absorb water and nutrients. The result is the intense vomiting and watery diarrhea norovirus is known for. Because the virus works so quickly and needs so few particles to establish an infection, a single sick person can easily set off an outbreak in a household, cruise ship, school, or nursing home.
Symptoms and Timeline
Symptoms typically begin 12 to 48 hours after exposure. The illness hits fast: most people go from feeling fine to sudden nausea, projectile vomiting, and watery diarrhea within a matter of hours. Stomach cramps, low-grade fever, muscle aches, and fatigue are common alongside the main symptoms.
The worst of it usually lasts 1 to 3 days. Most healthy adults recover without medical treatment, though you may feel drained for several days afterward. The biggest risk during this window is dehydration, especially for young children, older adults, and people with weakened immune systems. The CDC reports that norovirus causes roughly 109,000 hospitalizations and 900 deaths per year in the U.S., mostly among adults 65 and older.
How It Spreads
Norovirus spreads through direct contact with a sick person, contaminated food or water, and contaminated surfaces. Tiny droplets released during vomiting can become airborne and land on nearby surfaces or be inhaled by people standing close by. Shared food is another major route: an infected person preparing a meal can contaminate everything they touch.
One of the most frustrating aspects of norovirus is how long you remain contagious. Even after your symptoms resolve, you can continue shedding the virus for two weeks or more. That long tail of contagiousness is a major reason outbreaks are so difficult to contain, particularly in settings like hospitals and long-term care facilities where people share close quarters.
Why Some People Are Naturally Resistant
Not everyone who encounters norovirus gets sick, and genetics play a surprisingly large role. Your susceptibility depends partly on molecules called blood group antigens that sit on the surface of cells lining your gut. A gene called FUT2 controls whether these antigens are present. People with a functional version of this gene (called “secretors,” making up roughly 80% of the population) display these antigens, and the virus uses them as docking sites to enter cells.
People with an inactive FUT2 gene (“non-secretors”) lack those docking sites and are nearly completely resistant to the most common norovirus strain, known as GII.4. Challenge studies, where volunteers are deliberately exposed to the virus, have confirmed this protection. Prospective studies across countries including the U.S., Ecuador, Vietnam, and China have reinforced the finding.
This resistance isn’t universal, though. Several other norovirus genotypes can infect non-secretors just as easily as secretors. So while your genes may protect you from the dominant strain circulating in a given year, they won’t necessarily shield you from every version of the virus.
Why Hand Sanitizer Isn’t Enough
Alcohol-based hand sanitizers are a go-to for killing germs, but they perform poorly against norovirus. The reason traces back to the virus’s structure. Alcohol disrupts the fatty outer envelope that surrounds many viruses, like influenza. Norovirus has no envelope, so alcohol has far less to work with. Multiple studies have found that alcohol-based sanitizers are often ineffective against non-enveloped viruses like norovirus, and their use in outbreak-prone settings like long-term care facilities may give a false sense of security.
Washing your hands with soap and water for at least 20 seconds is the most reliable way to physically remove the virus from your skin. Soap doesn’t kill norovirus directly, but the friction and rinsing action wash particles away. This is one of the rare situations where old-fashioned handwashing clearly outperforms the convenience of a pump bottle of sanitizer.
Cleaning Contaminated Surfaces
Standard household cleaners often can’t inactivate norovirus. To properly disinfect a surface after someone has been sick, you need a chlorine bleach solution at a concentration of 1,000 to 5,000 parts per million. In practical terms, that’s 5 to 25 tablespoons of regular household bleach (5% to 8% concentration) mixed into one gallon of water. Alternatively, you can use a disinfecting product specifically registered with the EPA as effective against norovirus.
Any area where vomiting or diarrhea occurred should be cleaned immediately. Wear disposable gloves, wipe up the mess with paper towels, then apply the bleach solution and let it sit on the surface for at least five minutes before wiping it dry. Contaminated laundry, including towels and bedding, should be washed on the hottest appropriate cycle and machine-dried.
Staying Hydrated During Recovery
There’s no antiviral medication that targets norovirus. Recovery comes down to managing symptoms and, above all, replacing the fluids and electrolytes your body is losing. For most adults, that means drinking water, clear broths, sports drinks, or fruit juices in small, frequent sips, especially if vomiting makes it hard to keep anything down. Saltine crackers can also help replenish sodium.
Children are more vulnerable to dehydration because of their smaller body size. Oral rehydration solutions like Pedialyte are specifically designed for this situation, providing the right balance of glucose and electrolytes. Older adults and anyone with a weakened immune system should also use oral rehydration solutions rather than relying on water alone. Signs of severe dehydration, such as very dark urine, dizziness, dry mouth, or producing no tears when crying (in young children), need prompt medical attention. In serious cases, fluids may need to be given intravenously in a hospital.
Why Norovirus Keeps Coming Back
Unlike some viruses, norovirus doesn’t produce long-lasting immunity. Protection after an infection fades within a few months, and the virus mutates frequently enough that new strains regularly emerge. The dominant GII.4 genotype, which causes the majority of outbreaks worldwide, evolves in a pattern similar to influenza, producing updated variants every few years that can evade whatever partial immunity the population has built up. This is why people get norovirus multiple times throughout their lives, and why there is currently no vaccine available to prevent it.