The UK Health Security Agency (UKHSA) has warned there is a new strain of norovirus, which means people who have already fallen ill with the bug this winter could be infected again. The UKHSA sayshaving had one type of norovirus does not fully protect against other strains.
New lab data shows the recently discoveredGII.17 genotype of norovirus has seen a surge in cases this winter, and the older GII.4 variant is now on the rise. The GII.17 genotype remains dominant, accounting for 59% of cases. But in November it was responsible for 76% of cases.
The GII.4 strain now represents 29% of cases compared to just 10% three months ago.The UKHSA reassured people that there is no indication that either GII.17 or GII.4 leads to more severe illness but said it is unclear whether norovirus cases have peaked for this winter.
GII.17 and GII.4 both cause acute gastroenteritis. While their symptoms are generally similar, there are some differences in severity and affected populations.
Symptoms of GII.17 Norovirus
- Severe vomiting
- Diarrhoea
- Abdominal cramps
- Nausea
- Low-grade fever
- Fatigue
- Muscle aches
- Dehydration
GII.17 has been associated with more severe outbreaks, especially in older adults, and has a longer illness duration compared to some other norovirus strains.
Symptoms of GII.4 Norovirus
- Frequent vomiting
- Severe watery diarrhoea
- Nausea
- Abdominal cramps
- Headache
- Low-grade fever
- Dehydration
GII.4 is the most dominant and widespread strain globally and tends to mutate frequently, leading to new epidemic variants. It often affects all age groups and has caused large outbreaks in healthcare settings and cruise ships.
Both strains can cause acute gastroenteritis, lasting 12–72 hours, and are highly contagious. Dehydration is the most serious complication, so fluid replacement is essential.
Amy Douglas, lead epidemiologist at the 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.”
She added: “If you have diarrhoea and vomiting, please do not visit hospitals and care homes or return to work, school or nursery until 48 hours after your symptoms have stopped and don’t prepare food for others, as you can still pass on the virus during this time.Alcohol gels do not kill norovirus. Wash your hands with soapy warm water and clean surfaces with bleach-based products where possible to help stop infections from spreading.”
New data from NHS England shows hospital norovirus cases remain close to the record high seen last week, with an average of 1,134 patients per day in hospital compared to 1,160. The figure is more than double (up 141%) the same period last year (470).
NHS England said visits to the NHS.uk webpage on norovirus have risen by 40% in the last week – from 53,052 to 74,324.
UKHSA lab data shows confirmed cases in the two weeks from February 3 to 16 were 29.4% higher than the previous fortnight and more than double the five-season average for the same period. For every case reported in this national data, around 288 cases occur in the community, suggesting around three million cases in the UK.