Norovirus is the most common cause of infectious gastroenteritis worldwide and contributes significantly to winter pressures on the NHS and social care each year.
Also known as the ‘winter vomiting virus,’ norovirus is transmitted through the ingestion of viral particles and has a very low infectious dose, making it easily passed on through close contact with an infected person, contact with a contaminated object, or the consumption of contaminated food or water.
Symptoms, including vomiting, diarrhoea, fever, and muscle aches, are usually short-lived, lasting only 2 to 3 days, and typically resolve without medical treatment. However, vulnerable groups such as the very young, elderly, and immunocompromised are at risk of more severe or prolonged illness, which can lead to dehydration and may require hospital treatment.
Outbreaks often occur in closed settings such as prisons, nurseries, or schools, but the greatest impacts are seen in hospitals and care homes.
In these settings, ward closures, staff sickness, and disruptions contribute to significant winter pressures on the NHS. Previous studies estimate that norovirus outbreaks cost NHS inpatient services £298 million per year and result in around 30,000 bed days lost (1).
Since late 2023, norovirus laboratory reporting to national surveillance has been consistently higher than expected, with activity remaining high into the start of the 2024/2025 season. The cumulative total of norovirus laboratory reports since the start of the season in week 27, 2024, is more than double the 5-season average (3,425 compared to 1,491) (see Figure 1) (2).
During weeks 45 and 46, reports were nearly double (+98.6%) the 5-season average for the same period. Outbreaks reported to UKHSA in hospital settings are also 19.4% higher than the 5-season average (75 outbreaks compared to 63).
Figure 1. Norovirus laboratory reports in England by week during the 2023/2024 and 2024/2025 seasons, compared with the 5-season average*
*‘5-season average’ is calculated from the same period during the 5 prior seasons, excluding seasons impacted by the COVID-19 pandemic (2019/2020, 2020/2021, 2021/2022). The 2023/2024 5-season average is calculated from 2015/2016, 2016/2017, 2017/2018, 2018/2019, and 2022/2023; the 2024/2025 5-season average is calculated from 2016/2017, 2017/2018, 2018/2019, 2022/2023, and 2023/2024.
Activity is now increasing across all age groups, with the biggest rise in adults, particularly those aged 65 years and over. Compared to the 5-season average, this season’s age distribution has been more skewed towards adults, with 49.4% (+9.6%) of reports from cases in the 65+ group, 29.6% (+4.2%) in the 18 to 64 group, 15.6% (-13.5%) in children aged 0 to 4 years, and 4.8% in the 5 to 17 age group (comparable to the average).
While some of the increased reporting may be attributed to the wider use of PCR multiplex technology (capable of detecting multiple gastrointestinal pathogens in a single test) at frontline diagnostic laboratories, it is likely that the emergence of an unusual norovirus genotype, GII.17 (Figure 2), as well as changes in epidemiology following the COVID-19 pandemic, are contributing to the observed rise.
Figure 2. Trends of GII norovirus samples typed as genotype GII.17, GII.4, or another GII in England by season, 2017/18 to mid-November of the 2024/2025 season*
*Data for the 2024/2025 season is incomplete as it is only available up to week 45 (commencing 18 November 2024).
The usual escalation in reporting, typically seen each autumn, started earlier this season. Although there was a drop in reporting coinciding with the October half-term school holidays, reports are expected to continue increasing. While a shift in the timing of the seasonal increase does not always result in a higher peak of norovirus activity, the ‘unexpected’ activity could have more significant impacts on health and social care settings.
The latest data on norovirus is published weekly during the winter months as Official Statistics, and UKHSA guidance on how to prevent onward transmission is available at: Norovirus: What todo if you catch it and helping to stop the spread.
