Norovirus cases have risen to their highest seasonal level in five years amid a nationwide surge, alarming figures show.
UK Health Security Agency (UKHSA) chiefs received 1,237 laboratory-confirmed reports of vomiting disease in England in April.
It means fallen for this time of year are 75 percent above pre-Covid levels.
Health chiefs blamed 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 diarrhea, could be due to Covid restrictions and new strains.
UK Health Security Agency (UKHSA) chiefs received 1,237 laboratory-confirmed reports of vomiting disease in England in April. It means cases for this time of year are 75 per cent above pre-Covid levels
The disease can resemble the symptoms of Covid, with both viruses causing chills, fever and headache
The UKHSA figures show that most cases were among the over-65s.
The data is based on positive laboratory reports and NHS hospitals reporting suspected and confirmed outbreaks of norovirus. The actual number of cases 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: ‘Levels of norovirus in April were higher than we would normally see at this time of year, and have increased.
‘This is probably due to a combination of factors, but the colder weather we have had will not have helped.
‘Norovirus can cause dehydration, especially in vulnerable groups such as young children and older or immunocompromised people. If you do become ill, it is important to drink enough.
“If you have diarrhea and vomiting, you can take steps to avoid passing on the infection.”
She added: ‘Do not return to work, school or nursery until 48 hours after your symptoms have resolved and do not prepare food for others during that time.
‘If you are feeling unwell, do not visit people in hospitals and care homes to avoid passing on the infection in these settings.
Washing your hands with soap and warm water and using bleach-based products to clean surfaces can also prevent infections from spreading.
‘Alcohol gels don’t kill norovirus, so don’t rely on them alone.’
Experts today suggested that Covid restrictions could also be partly responsible for the current surge, as fewer people than normal have been exposed to norovirus since the start of the pandemic.
According to their theory, our bodies may be less equipped to fight the infection after years of little exposure to it.
The same reason was partly attributed to the unprecedented spike in scarlet fever cases, which ballooned in 2022 to the highest number since the 1950s.
But they also warned that 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 higher than usual recent figures may still be related, at least in part, to the decline in numbers during the Covid lockdown period.
‘We continue to see unusual epidemiology in terms of the number of cases and the seasonality of numerous infections following the pandemic.
‘The relatively bad weather in the spring may also have contributed to this.
‘Sometimes we see the emergence of new strains of norovirus against which people have little or no immunity from previous infections.
‘About 17 percent of the very recent cases are due to a strain called G.II.17, which has only emerged quite recently. So this may also contribute to the higher than usual number of cases.’
He added: ‘There are also vaccines on the horizon, one of which is about to announce results from 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, associate professor of virology at the London School of Hygiene & Tropical Medicine, told MailOnline that the ‘unusual increase’ in cases ‘is an interesting and important observation’.
He added: ‘Norovirus is a diverse group of viruses with many different types.
Experts today suggested that Covid restrictions could also be partly responsible for the current surge, as fewer people than normal have been exposed to norovirus since the start of the pandemic. According to their theory, our bodies may be less equipped to fight the infection after years of little exposure to it
‘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 last long.’
He said: ‘There is a lot we still don’t understand about how people respond to norovirus infection and how responses to one type of norovirus compare to others.
‘Other important factors are that we still do not fully understand the ongoing changes in norovirus epidemiology following the Covid pandemic.
‘Changes in sampling, testing and reporting patterns for national surveillance systems could impact data in ways that are difficult to monitor.’
Norovirus can increase pressure on hospitals, as infected patients must be isolated in single rooms or wards closed to new patients to limit the spread.
Symptoms include nausea, vomiting and diarrhea, while some patients may also have fever, headache and sore arms and legs.
Most people get better within two to three days and can manage their condition at home by resting and drinking plenty of fluids.
However, severe cases may require some people to be hospitalized, while the elderly and children are most at risk.