In January 2022, doctors in Scotland noticed a worrying trend: a scattering of cases of severe hepatitis in kids between 1 and 5 years old. The children were presenting with gastrointestinal symptoms—abdominal pain, diarrhea, vomiting—followed by the onset of jaundice. To see such acute hepatitis (a broad term that essentially describes inflammation of the liver) in young, previously healthy children was highly unusual—and a cause for concern.
By April 5, the Scottish health authorities had recorded 11 cases. Unable to pin down their cause, they notified the World Health Organization, kicking off a global investigation that has left health authorities searching for answers.
Cases were immediately picked up across Europe— in Denmark, France, the Netherlands, Ireland, Romania, and Spain—as well as in Israel and the US. On April 12, the European Centre for Disease Prevention and Control instructed its hepatitis network to keep an eye out for further cases fitting the description. Since then, case counts have continued growing. The UK has now reached a total of 114 cases, with 10 children requiring a liver transplant. In total, at least 190 cases have been logged in at least 12 countries. One child has died.
But experts still aren’t sure what is responsible for these cases.
Hepatitis can be caused by exposure to a toxin or a drug (an overdose of Paracetamol can trigger liver damage, for instance). But toxicology screenings haven’t turned up anything that looks like a probable explanation.
So could a viral infection be to blame? Acute forms of viral hepatitis are typically caused by an infection with one of the five hepatitis viruses: A, B, C, D, and E. It’s not unusual to see cases of hepatitis following an infection with one of these viruses—but in children, this generally occurs when they are immunosuppressed. “The unusual thing is that it’s happening so frequently, in such a short period of time, in generally well children,” says Connor Bamford, a virologist at Queen’s University Belfast. However, hepatitis viruses weren’t detected in any of the kids, and so can be ruled out.
But one common viral suspect did keep turning up in tests: adenovirus. This family of common viruses is one of the main causes of the common cold, and around three-quarters of the British children who’ve fallen ill have tested positive for one. Specifically, adenovirus F41 has been singled out, having been detected in multiple children’s blood tests, although other adenoviruses have been detected as well. “The strongest evidence is for adenovirus, because it’s just one of the most consistent things that they’ve seen,” says Bamford.
But what isn’t adding up is the fact that an adenovirus infection is usually pretty mild. Although adenoviruses can cause hepatitis on rare occasions, this isn’t something they’re known for. One theory is that a mutated form of adenovirus could be circulating, which would explain why reactions are more severe than usual.
There’s also another speculation: “that actually, it’s just the same virus that we’ve always had, but because of the lockdown, and decreased interactions between people, there was less of the virus spreading,” says Bamford. The idea is that by having less exposure to viruses in general throughout the pandemic, children haven’t had a chance to build up the immunity they normally would through smearing germs on one another in the playground—meaning more severe illness when they are eventually exposed. However, some evidence from the UK suggests adenoviruses never really stopped circulating during the pandemic, so it’s unclear to what degree children really have been underexposed.