Norovirus cases are surging across the UK as spring approaches, with the average number of patients hospitalized with the illness reaching over 1,000 per day for the first time this winter, according to NHS England. The latest figures show 1,012 patients in hospital with norovirus each day during the most recent reporting week, representing a nearly 10 percent increase from the previous week. This marks the second consecutive week of rising norovirus infections, prompting hospitals to close wards in an effort to contain outbreaks.
Health officials have expressed surprise at the sustained rise in norovirus cases, particularly as cases of flu and other respiratory viruses begin to decline. The illness, often called the winter vomiting bug or the two-bucket virus due to its dual symptoms of diarrhea and vomiting, typically peaks during colder months but rarely continues escalating this late in the season.
Why Norovirus Cases Continue to Rise
According to Andrew Easton, a professor of virology at the University of Warwick, the continued surge in infections is not entirely clear. While respiratory viruses such as COVID-19, respiratory syncytial virus, flu and the common cold are declining from their peak levels, norovirus has moved in the opposite direction. The virus causes symptoms including nausea, vomiting, diarrhea, high temperature, abdominal pain and aching limbs.
The highly infectious nature of norovirus contributes significantly to its rapid spread. It takes fewer than 100 viral particles to cause infection, while infected individuals shed billions of particles in their stools and vomit. Additionally, the virus has an incubation period of 12 to 48 hours, meaning people often unknowingly transmit the illness before symptoms appear.
Multiple Strains Circulating Simultaneously
One leading theory for the sustained outbreak involves multiple mutations of norovirus circulating at the same time. According to a study published in Nature Communications, genotype GII.17 has surged over the past two years and possesses the ability to mutate quickly enough to infect people multiple times. Meanwhile, strains of the GII.4 genotype, which caused 70 to 80 percent of all reported outbreaks between 2006 and 2016, remain in circulation.
Professor Easton explains that when multiple genotypes circulate simultaneously, individuals may be susceptible to reinfection within the same season. Having immunity to one strain does not provide full protection against other variants. This phenomenon has also been observed with RSV, according to the expert.
Environmental and Health Factors Contributing to Spread
Persistently wet weather throughout the UK has kept people indoors, creating ideal conditions for viral transmission. In poorly ventilated rooms, the amount of virus in the air can build up, increasing the risk of spread, according to Professor Peter Openshaw, a respiratory physician at Imperial College London. The risk of airborne transmission increases when occupants participate in energetic activity or when they are shouting, singing or talking loudly.
However, other circulating infections may also play a role in the norovirus surge. A 2022 study published in The Lancet found that among nearly 7,000 hospital patients with COVID-19, 583 also had flu, RSV or adenoviruses. Professor Openshaw notes that developing one virus can reduce immune defenses to other illnesses, and developing more than one virus simultaneously can lead to more severe outcomes.
Long-Term Impact of COVID-19 Lockdowns
Professor Easton suggests that COVID-19 lockdowns may still be affecting immunity levels. Two years of reduced exposure to flu and other respiratory infections due to isolation and mask-wearing may have resulted in reduced general immunity to these viruses even now. This lowered immunity could be contributing to the sustained high levels of various viral infections, including norovirus.
There is currently no vaccine available for norovirus, unlike flu and RSV. For those wanting to protect themselves against other circulating viruses, NHS flu jab appointments remain available until March 31, 2026. RSV vaccinations are currently limited to pregnant people, those aged 75 to 79, or individuals who turned 80 after September 1, 2024, though eligibility may soon expand to more vulnerable populations.
Health officials continue to monitor norovirus infection rates closely, though no specific timeline has been announced for when cases might decline. Authorities have not confirmed whether additional public health measures will be implemented if hospitalization numbers continue to rise.
