Almost 200 cases of severe and unexplained hepatitis have been recorded in children worldwide.
Scientists are trying to determine what exactly is causing the outbreak, which has affected around 190 children so far.
Severe hepatitis, an inflammation of the liver usually due to a viral infection, is rare in children who are otherwise healthy.
The outbreak is now affecting children in at least 12 countries, including in Canada, Japan, the US and Israel.
The first case was reported in the United Kingdom in April and 111 children, for the most part younger than 10-years-old, have been found to have the disease.
According to the European Centre for Disease Prevention and Control (ECDC) around 190 unexplained cases of severe hepatitis have been reported in children around the world.
Of these, some 40 cases have been recorded in the European Union and the European Economic Area.
The ECDC is currently investigating the outbreak as is the World Health Organisation (WHO).
Unusually, the new cases do not seem to feature the viruses which are typically responsible for acute liver inflammation. These are hepatitis A, B, C, D and E.
So far, 17 children have needed liver transplants as a result of the recent cases. One child has died, the WHO reports.
Many of the children with hepatitis suffered symptoms such as abdominal pain, diarrhoea and vomiting. Many also suffered from jaundice, where the liver is damaged and the skin and eyes appear yellow.
As yet, scientists are unsure what exactly is behind the rapid rise in cases of hepatitis among children.
Viruses known as adenoviruses were detected in more than 70 of the children, while Covid-19 was also detected in 20 cases.
However, the WHO said in a recent report that although adenovirus is one hypothesis as the underlying cause, “it does not fully explain the severity of the clinical picture.”
The strain of adenovirus, known as type 41, that is being seen in many of the children, was not previously linked to severe hepatitis.
“While there have been case reports of hepatitis in immunocompromised children with adenovirus infection, adenovirus type 41 is not known to be a cause of hepatitis in otherwise healthy children,” the WHO said.
Dr Andrea Ammon, Director of the European Centre for Disease Prevention and Control, told reporters in a briefing on Tuesday that another hypothesis investigated is whether or not lockdowns could have weakened children’s immunity as they were not exposed to as many pathogens.
The WHO said “hypotheses related to side effects from the Covid-19 vaccines are currently not supported” given that the majority of children affected had not received a Covid-19 vaccination, due to them being too young.
They went on to add: “Other infectious and non-infectious causes need to be thoroughly investigated.”
