What actually works to prevent norovirus, the winter stomach bug

Norovirus — the cause of most winter-vomiting outbreaks on cruise ships, in schools, hospitals and care homes — is a masterclass in why some infections are so hard to stop. Almost every property that makes a pathogen contagious, norovirus has, and understanding those properties is the fastest route to knowing which precautions are worth the effort and which are theatre. The short version: the measures that work are the boring, physical ones, and several popular defences do very little.

Why it is so hard to avoid

Start with the dose. A review in Clinical Microbiology Reviews describes norovirus as having an extremely low infectious dose — it takes only a small number of viral particles to make someone ill [s1]. Modelling work published in the Journal of Medical Virology estimated that dose at the level of a few tens of particles, meaning an amount of contamination far too small to see or taste can be enough to infect [s2]. For comparison, an infected person sheds virus in enormous quantities, so the ratio of "amount shed" to "amount needed" is wildly lopsided in the virus's favour.

Then there is durability. Norovirus is a non-enveloped virus, and that structural detail has an outsized practical consequence: it makes the virus resistant to many common disinfectants and to alcohol-based hand sanitiser, and lets it persist on surfaces and in the environment for days [s1]. This is the single most important thing to know about preventing it, and it overturns a common habit. The alcohol gel that works well against enveloped viruses such as influenza is much less effective against norovirus [s1]. Reaching for hand gel after caring for a sick person can create a false sense of safety.

What actually works

Against that biology, the effective defences are the physical ones. Handwashing with soap and water is the recommended approach precisely because it does not rely on chemically killing the virus — it physically removes it from the hands and rinses it away, which alcohol gel cannot do [s1]. The mechanical action and the rinse are doing the work. The broader evidence that hand hygiene reduces the spread of infections is consistent with this: a 2023 Cochrane review found that hand-hygiene measures probably modestly reduce transmission, while being honest that the size of the effect is uncertain and varies by setting [s3]. Modest and reliable beats dramatic and false.

Surface cleaning follows the same logic. Because norovirus survives on surfaces and resists mild disinfectants, ordinary wiping is not enough for contaminated areas; a chlorine-based (bleach) disinfectant is the standard recommendation for cleaning up after vomiting or diarrhoea, as it is effective where alcohol and many other agents are not [s1]. Vomiting itself aerosolises the virus and can contaminate a wide area, which is why outbreaks spread so explosively in enclosed settings and why prompt, thorough cleaning of the whole affected area matters [s1].

Two more measures come straight from the virus's behaviour. Infected people continue to shed virus after they feel better — shedding can persist for a period beyond the resolution of symptoms — which is the evidence basis for the common advice that people stay away from work, school and especially food handling for a couple of days after recovering [s1]. And because food and water are major transmission routes, careful food hygiene, particularly with shellfish and with food prepared by someone recently ill, closes another door [s1].

What matters less than people think

The through-line is that norovirus prevention is counterintuitive because the intuitive tool — hand gel — is one of the weak ones [s1]. There is also no widely available vaccine yet, though candidates are in development, so prevention rests entirely on breaking the transmission routes [s1]. The defences with the best evidence are unglamorous: soap and water over gel, bleach over ordinary cleaners for contaminated surfaces, staying away from others for a couple of days after recovery, and food and water hygiene. That is not a coincidence. Each of them targets a specific property of a virus built to exploit the shortcuts people take. This explainer describes prevention; anyone who is severely ill or dehydrated, particularly a young child or older adult, needs medical assessment.