Norovirus cases have soared to their highest seasonal level in five years amid a nationwide surge, alarming figures suggest.
UK Health Security Agency (UKHSA) chiefs received 1,237 lab-confirmed reports of the vomiting bug in England in April.
It means cases for this time of year are 75 per cent above levels seen pre-Covid.
Health chiefs blamed the rise on the recent spell of cold weather and warned people not to work for at least 48 hours after symptoms end.
Experts also suggested the spike in norovirus, which can also cause diarrhoea, could be a result of Covid restrictions and new strains.
UK Health Security Agency (UKHSA) chiefs received 1,237 lab-confirmed reports of the vomiting bug in England in April. It means cases for this time of year are 75 per cent above levels seen pre-Covid
The illness can appear similar the symptoms of Covid, with both viruses causing chills, fever and headaches
The UKHSA figures show most cases were among the over-65s.
Its data is based on positive laboratory reports and NHS hospitals reporting suspected and confirmed norovirus outbreaks. Actual case numbers will be even higher.
By contrast, there were 4,027 lab-confirmed reports at the end of January, when the bug is typically at its peak
Amy Douglas, a norovirus epidemiologist at the UKHSA said: ‘Norovirus levels were higher in April than we would usually see at this time of year and have been increasing.
‘This is likely due to a combination of factors, but the colder weather we have had won’t have helped.
‘Norovirus can cause dehydration, especially in vulnerable groups such as young children and older or immunocompromised people, so if you do get ill it is important to drink plenty of fluids.
‘If you have got diarrhoea and vomiting, you can take steps to avoid passing the infection on.’
She added: ‘Do not return to work, school or nursery until 48 hours after your symptoms have stopped and don’t prepare food for others in that time either.
‘If you are unwell, avoid visiting people in hospitals and care homes to prevent passing on the infection in these settings.
Washing your hands with soap and warm water and using bleach-based products to clean surfaces will also help stop infections from spreading.
‘Alcohol gels do not kill norovirus so don’t rely on these alone.’
Experts today suggested Covid restrictions could also be partly to blame for the current surge, as fewer people have been exposed to norovirus than usual since the start of the pandemic.
Our bodies may be less well-equipped to fight off the infection after years with little exposure to them, according to their theory.
The same reason was partly blamed for the unprecedented spike in scarlet fever cases, which in 2022 ballooned to the highest number reported since the 1950s.
But they also cautioned new strains of the bug could be behind the rise.
Professor Adam Finn, a member of the Government’s vaccine advisory panel, at the University of Bristol, told MailOnline: ‘The larger than usual recent numbers may still be related, at least in part, to the drop in numbers during the Covid lockdown period.
‘We are still seeing unusual epidemiology in terms of numbers of cases and seasonality of numerous infections, post pandemic.
‘The relatively poor weather during the spring may also have contributed.
‘Sometimes we see emergence of new strains of norovirus against which people have little or no immunity from previous infections.
‘Around 17 per cent of the very recent cases have been due to a strain called G.II.17 which has only emerged quite recently. So this too may be contributing to the higher than usual number of cases.’
He added: ‘There are also vaccines on the horizon with one about to announce results of a phase three trial.
‘So, we may have the tools to prevent or at least reduce this problem in the not-too-distant future.’
Meanwhile, Dr David Allen, an associate professor in virology at the London School of Hygiene & Tropical Medicine, told MailOnline the ‘unseasonal rise’ in cases ‘is an interesting and important observation’.
He added: ‘Norovirus is a diverse group of viruses with many different types.
Experts today suggested Covid restrictions could also be partly to blame for the current surge, as fewer people have been exposed to norovirus than usual since the start of the pandemic. Our bodies may be less well-equipped to fight off the infection after years with little exposure to them, according to their theory
‘People can get norovirus many times because infection with one type of norovirus may not protect against the other types, and protective immunity after infection may not be long-lasting.’
He said: ‘There is a lot we still do not understand about how people respond to norovirus infection and how responses to one type of norovirus relate to others.
‘Other important factors are that we still do not fully understand the ongoing changes to the epidemiology of norovirus following the Covid pandemic.
‘Changes in sampling, testing and reporting patterns to national surveillance systems can influence data in ways that are hard to monitor.’
Norovirus can pile pressures on hospitals because infected patients need to be isolated in single rooms or wards need to be closed to new patients to contain the spread.
Symptoms include nausea, vomiting and diarrhoea, while some sufferers may also have a fever, headache and aching arms and legs.
Most people get better within two to three days and can manage their condition at home through rest and drinking plenty of fluid.
However, in severe cases, some people may need to be hospitalised with the elderly and children most at-risk.
