A vaccine is to be tested on thousands of people to find out whether it can protect against norovirus – a stomach worm that causes vomiting and diarrhoea.

The easily spread winter virus can affect people of all ages and have major consequences – often closing hospital wards, pulling children out of school and keeping parents out of work.

The vaccine will be tested on about 25,000 adults, mostly over the age of 60, in more than six countries around the world over the next two years.

If successful, researchers say it would reduce the number of vulnerable adults in hospital during the winter, as well as reduce the financial burden on health systems like the NHS.

Vaccines against viruses such as flu, Covid and RSV already exist and protect millions of people every year – but no vaccine has ever been licensed against it. norovirus,

The vaccine that is being trialed has been made by Moderna and it is an mRNA vaccine. Like the company’s Covid jab, it instructs our immune system how to recognize an invading virus and defend against it by producing antibodies.

The tricky thing about norovirus is that it is difficult to detect.

“There is wide and changing diversity of genotypes over time,” says Dr Patrick Moore, a GP in Dorset and lead investigator of the study.

Therefore this vaccine contains the three most common types of viruses to achieve the best results.

There are still many unknowns – for example, how long will the protection last, how effective will it be, and how often will the vaccine need to be updated?

Those questions need to be answered during the trial, which is a collaboration between the UK government, the National Institute for Health and Care Research (NIHR) and Moderna.

Twenty-seven NHS hospitals and centers in England, Scotland and Wales will take part in the trial, half of whom will be given the vaccine, and in better health than the other volunteers.

Researchers will also look for side effects of the vaccine.

The impact of norovirus on Britain is considerable.

It has a human cost – every year, about four million people are infected by disease-causing insects, with 12,000 hospitalized with it and 80 deaths.

The financial cost to the NHS is approximately £100 million annually.

Those who are most at risk are often older adults and the most vulnerable, including care home residents. But health care workers, child care workers, flight attendants and cruise ship passengers and crews are also often affected.

The only treatment for norovirus is to drink plenty of fluids, to avoid dehydration.

Saul Faust, professor of pediatric immunology and infectious diseases at the University of Southampton, said that norovirus has “put a huge burden on health care systems”.

“Any infection increases frailty – and this is difficult to reverse in older populations,” he said.

Mobile units will be used in the trial so that researchers can go to care homes and give the vaccine to more people.

Ultimately, if the vaccine shows at least 65% efficacy, and further trials occur, Professor Faust said it could also be used to protect children.

But this is likely to take several years. In the meantime, researchers are focusing on gathering data that shows the vaccine reduces people’s risk of getting sick from norovirus. They will then send this information to the UK regulator to get approval for the jab.

Health and Social Care Secretary Wes Streeting said norovirus puts the NHS under “huge strain every winter”.

“The UK is leading the way in developing the world’s first vaccine for this vomiting bug,” he said.

Professor Lucy Chappell, chief executive of the NIHR, said the vaccine could make a difference to the lives of many people, “especially our most vulnerable citizens”.

Several other pharmaceutical companies are developing norovirus vaccines, including Hilavax and Vaxart.