February 27, 2025

expert reaction to UKHSA warning of potential second norovirus wave

Scientists comment on the potential of a second norovirus wave. 

Dr Damien Tully, Associate Professor at the Medical Research Council/Uganda Virus Research Institute and London School of Hygiene & Tropical Medicine (MRC/UVRI and LSHTM) Uganda Research Unit, said:

“Since 2012, there has been one dominant norovirus variant circulating in the UK called GII.4. The surge in norovirus activity this season is due to a new variant of a different type of norovirus called GII.17 which, over the last seven years, has circulated at low levels and has only been responsible for around 1% of cases.

“Given the current variant’s low prevalence over past years, most people are susceptible to infection, which explains the huge surge in cases. Similarly, we know that infection with the variant that has previously caused the majority of cases (GII.4) will not confer any immunity to other strains of norovirus, so those who have experienced infection will still be susceptible to other strains.

“Reduced population immunity due to lower exposure during COVID-19 may have also created an environment where multiple strains can spread more easily.

“The second wave, while a cause for concern, should not be entirely surprising, as the GII.4 strain has dominated for over a decade and is a tough competitor. Time will tell if the new GII.17 variant can end GII.4’s 12-year reign as the dominant strain.

“The secret behind GII.17’s sudden success is still under investigation but through our research, we are continuing to find clues from the virus’s genome that may explain why it’s behaving differently. The new strain is evolving between 3 and 6 times faster compared to other GII.17 variants and changes to its structure may be affecting its ability to infect us.

“Uncovering the clues to norovirus’s success will help us unlock the potential for a vaccine, hopefully in the near future.

“The best advice is to be diligent with hand washing with soap and warm water, as alcohol-based hand sanitisers or gels do not kill the virus. Norovirus can also survive on surfaces for days but bleach or other disinfectants are effective against it.

“While to most of us infection with norovirus may just be annoying, it can have significant consequences for vulnerable groups, like the elderly, and for those whose job requires them to be in contact with many people a day, like healthcare workers. So any step you can take in preventing norovirus spread is important.”

Prof Paul Hunter, Professor in Medicine, University of East Anglia

How concerning is this potential second wave of norovirus?

“A double peak for norovirus is not unusual. We saw the same thing last winter and in 2020/21 winter but not so much in 2022/23.

How unusual is it to see two different strains within a season?

“Not at all unusual and indeed is the norm, though one tends to predominate.

“A year ago 83% were genogroup 2 (GII) and 17% (127 out of 770) were genogroup 1 (GI). The most frequent norovirus GII genotypes identified were GII.4 (42%) and GII.3 (19%), the most frequently identified norovirus GI genotypes were GI.3 (8%) and GI.6 (4%).

“Two years ago 90% were genogroup 2 (GII), 8% were genogroup one (GI) and 2% were mixed. The 3 most frequent norovirus GII genotypes identified were GII.4 (48%), GII.3 (13%) and GII.2 (10%) and the most frequently identified norovirus GI genotypes were GI.3 (3%) and GI.6 (3%).

“So we usually see quite a variety of genotypes each year.

How does this pattern compare to previous/ typical years?

“It is following roughly the same pattern as previous years more or less but somewhat greater number of cases.

“So far this season (2024/25) up to week 7 the cumulative number of positive norovirus laboratory reports stands at 9,289 in England.

“The equivalent number last year up to week 7 was only 4,855 and the year before that 4,551. So this represents quite a jump.

Do we know what causes something like this to happen?

“I don’t think we really know why such infections are as high this year

“Partly it will be down to better diagnostics. Testing for norovirus has become increasingly common in recent years as a result of new technology and so some of this increase will be an artifact of increased testing.

“Low population immunity as a result of low infection levels as a result of the covid controls will also be playing a role.

“There may well be some impact due to different variants becoming prominent in much the same way as we saw with covid variants, although there is no really new variant of norovirus as far as I can tell.”

Professor Arlene Wellman MBE, Group Chief Nurse for St George’s, Epsom and St Helier, said:

“Once norovirus enters a hospital, it can rip through our wards like wildfire, making patients even sicker. We are doing everything we can to limit the spread, but you can help us.

“Hand sanitisers such as alcohol gel do not kill the bug – the simple act of good hand washing with soap and water can make all the difference between our beds being used to care for patients, or lying empty at a time when every bed is precious.”

https://ukhsa-newsroom.prgloo.com/news/ukhsa-warns-of-potential-second-norovirus-wave

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