Norovirus FAQ: Your Questions Answered

Norovirus is most contagious when you are actively sick and during the first few days after you recover. Per CDC guidance, the virus can be found in your stool for 2 weeks or more after you feel better, meaning you can still spread the virus to others even when you feel completely well.

The CDC recommends not preparing food for others for at least 48 hours after symptoms resolve. Immunocompromised individuals may shed the virus for weeks to months.

Yes. Unlike many viral infections, norovirus does not confer long-lasting immunity. After infection, most people develop some protection against the specific strain that infected them — typically lasting 6 months to 2 years. However, you can be reinfected by a different norovirus strain or by the same strain once your immunity wanes.

This is why some people seem to get norovirus "every year" — they are likely being infected by different strains or reinfected after immunity fades. There is also some evidence that certain people with specific blood group antigens (particularly those who are blood type O) are more susceptible to GII.4 norovirus strains.

Alcohol-based hand sanitizers are less effective against norovirus than soap and water. The CDC specifically recommends washing hands with soap and water for at least 20 seconds as the preferred method of hand hygiene when norovirus exposure is possible.

This is because norovirus is a non-enveloped virus — it lacks the lipid membrane that makes many other viruses (like influenza and coronaviruses) susceptible to alcohol disinfection. The physical scrubbing action of handwashing with soap removes viral particles from the skin more effectively.

Hand sanitizers may be used when soap and water are genuinely unavailable, but should not be relied upon as primary protection during norovirus outbreaks.

Norovirus is the most common cause of what people colloquially call "stomach flu," "stomach bug," or "a 24-hour bug." However, the term "flu" technically refers to influenza, a respiratory illness caused by influenza A or B viruses. The two conditions are not related.

Norovirus causes gastrointestinal symptoms (nausea, vomiting, diarrhea). Influenza primarily causes respiratory symptoms (cough, congestion, sore throat) along with fever and body aches. You can have both infections simultaneously, but they are distinct diseases caused by different viruses.

Norovirus contaminates food through two main pathways. The most common is an infected food handler who touches ready-to-eat food without properly washing hands. Because the infectious dose is so small (as few as 18 viral particles), even a tiny amount of contamination can cause illness in many people simultaneously.

The second major foodborne route is shellfish, particularly raw oysters, clams, and mussels. These filter-feeding animals concentrate norovirus from contaminated water. Shellfish from sewage-contaminated growing areas carry significant norovirus risk, and even cooking does not guarantee complete inactivation — thorough cooking to 145°F (63°C) internal temperature is required, and some risk remains with raw shellfish.

Norovirus is remarkably stable in the environment. On hard, non-porous surfaces (like countertops, door handles, and toilet seats), norovirus can survive for days to weeks under the right conditions. On soft surfaces like carpet, it may survive for hours to days.

The virus also survives freezing temperatures, meaning frozen food contaminated with norovirus remains infectious after thawing. Standard household disinfectants containing chlorine bleach are required to inactivate norovirus on surfaces — many common disinfectants (including those based on quaternary ammonium compounds alone) are not reliably effective.

For most otherwise healthy pregnant women, norovirus illness follows the same course as in non-pregnant adults and resolves within 1–3 days. The primary concern is dehydration, which can affect both the mother and fetus.

Pregnant women who cannot keep any fluids down, experience reduced fetal movement, or have symptoms lasting more than 2–3 days should contact their healthcare provider. Severe dehydration may require IV rehydration. There is no evidence that norovirus itself crosses the placenta or directly harms the developing fetus.

Most otherwise healthy adults and older children with norovirus illness do not need emergency care. Home management with oral rehydration is appropriate for mild-to-moderate illness.

Seek emergency care if you or someone you are caring for experiences: inability to keep any fluids down for more than 24 hours, signs of severe dehydration (no urination for 8+ hours, extreme dry mouth, confusion, rapid heart rate), blood in stool or vomit, fever above 102°F (38.9°C) persisting more than 24 hours, or symptoms lasting more than 3 days without improvement. Infants, elderly adults, and immunocompromised individuals have a lower threshold for seeking care.

As of 2026, there is no approved norovirus vaccine. Several candidates have entered clinical trials, with Takeda's TAK-214 (targeting GII.4 and GI.1 strains) among the most advanced. Early phase results showed promising immunogenicity and some efficacy, but no vaccine has completed Phase III trials with sufficient data for regulatory approval.

Development is complicated by the rapid evolution of norovirus strains, the short duration of natural immunity, and the need to demonstrate efficacy across multiple genotypes. A vaccine would likely be most valuable for protecting elderly populations in long-term care facilities, food handlers, and travelers to high-risk areas.

Human noroviruses (GI and GII) do not infect dogs, cats, or other common household pets. Animals have their own calicivirus strains that can cause illness in them, but these do not cause norovirus illness in humans.

However, pets can theoretically act as mechanical vectors — meaning a pet could carry norovirus on its fur or paws after contact with contaminated surfaces, and then transfer it to human hands. This is considered a low-probability transmission route, but it's a reason to maintain good handwashing habits around animals as well.