What is norovirus? Symptoms of GII.4 strain and how long is the incubation period as hospitals issue warning

• Cases of norovirus are more than double the five-season average for the same four week period.
• Some hospitals across the UK are deciding to restrict visitors in a bid to curb the outbreak.
• The UK Health and Security Agency have warned of a potential second wave, with those who had norovirus during winter potentially at risk again.
• The two dominant strains of norovirus in the UK are GII.17 and GII.4.
• Hospitals are warning anyone who has norovirus symptoms to stay at home.

Norovirus cases have continued to increase across the UK, with the number of outbreaks reported to the Hospital Norovirus Outbreak Reporting System (HNORS) during weeks 14 to 17 nearly double (43.3%) the five-season average.

This has lead to some hospitals, including Southport Hospital and Bedford Hospital in Fort William bringing in visitor restrictions and urging that those with symptoms “do not attend the hospital unless it is a medical emergency”, in a bid to curb the outbreak.

The UK Health and Security Agency (UKHSA) have warned of a potential second wave, with those who had norovirus during winter potentially at risk again. As the dominant strain of norovirus infections has changed from GII.17 to GII.4.

Hospitals in some areas of the UK have been restricting visitors over a rise in the cases of norovirus. | Pexels, Andrea Piacquadio

Amy Douglas, Lead Epidemiologist at UKHSA, said: “Norovirus levels are still exceptionally high and now with multiple genotypes spreading at the same time, people could end up getting infected more than once this season. We are seeing the biggest impacts in health and social care settings, such as hospitals and care homes.”

What is norovirus?

Norovirus, is a stomach bug which can cause vomiting and diarrhoea. It is also known as the winter vomiting bug, however despite this name you can get norovirus at any time of the year.

What is norovirus Gll.4?

The two most common strains that are causing norovirus infections in the UK are Gll.4 and Gll.17. During the 2024/2025 season to date, Gll.17 was the most frequently identified strain, making up 51.1% of cases, whilst GII.4 is now made up 29.8% of cases, rising sharply from just 10%.

This means that people who have previously had norovirus may be susceptible to catching it again as having one strain of norovirus does not fully protect you against the other.

What are the symptoms of norovirus?

Despite the different strains, the symptoms of norovirus remain the same, common symptoms include:

• nausea and vomiting
• diarrhoea
• high temperature
• abdominal pain
• aching limbs

Young children, older adults and those with weakened immune systems are more likely to develop severe symptoms, which can cause dehydration. Anyone with these symptoms should drink plenty of fluids.

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How long is the norovirus incubation period?

Norovirus has a quick incubation period, with those who have been exposed to the virus typically becoming unwell within 12 to 48 hours.

Is norovirus contagious?

Norovirus is highly contagious and can easily spread between people. You can catch norovirus from close contact with someone who has it, touching surfaces or objects that have norovirus on them and then touching your mouth or eating food that has been prepared or handled by someone with norovirus.

How can you prevent norovirus?

To help prevent catching norovirus wash your hands with soap and warm water, alcohol hand gels do not kill norovirus and cannot offer you protection.

If someone in your home has norovirus wash any contaminated clothing and bed linen at 60°C, remember to wear disposable gloves to prevent catching the virus and use bleach-based household cleaners to help disinfect surfaces.

When can you return to work after norovirus?

If you have norovirus you should stay off school or work until you have not vomited or had diarrhoea for at least two days to prevent spreading the virus.

You also should not visit others in hospitals or care homes until you have not been sick or had diarrhoea for two days, as this will help prevent you from spreading the virus to those who are more vulnerable.

You can find out more about norovirus signs and how to ease symptoms at NHS.UK.