Health officials are urgently investigating the rise in cases which has led to more than 100 children needing hospital care and liver transplants for 10 British children.
Since the start of the year, 111 children have required hospital care for liver inflammation (hepatitis), with the majority of cases occurring among children under the age of five.
The leading line of inquiry is that the cases are being fuelled by a common virus called the adenovirus.
‘My hiccups and indigestion turned out to be caused by cancer’
Vegetarian women more likely to fracture hips in later life, study shows
Which side of the bed do you sleep on? Here’s what it says about your personality
Call to protect our vulnerable as temperatures to rise to 28 °C
Coroner rules no link established between teenager’s sudden death and MR vaccine
This virus usually causes mild illnesses including stomach upsets and colds.
But one theory is that the virus is leading to more severe illness among some children due to “susceptibility, for example due to lack of prior exposure during the pandemic”, according to a technical briefing from the UK Health Security Agency (UKHSA).
Of 53 cases tested, 40 (75%) showed signs of adenovirus infection.
Routine NHS and laboratory data show that common viruses circulating in children are currently higher than in previous years and there is a marked increase of adenovirus, particular in the one to four age group, the UKHSA said.
Other avenues being explored include whether a prior Covid infection followed by an adenovirus infection could be leading to more severe cases or co-infection with the two viruses.
Experts are also examining other possible causes including a new variant of adenovirus; potential exposure to drugs, toxins or environmental factors; a new type of infection; or a new variant of the virus which causes Covid.
Covid-19 vaccination is not a contributing factor as none of the cases investigated so far have been vaccinated.
The cases are predominantly in children under five who showed initial symptoms of diarrhoea and nausea followed by jaundice.