Two teenagers in the Netherlands have ended up in intensive care after being hit by a mystery illness, including fever, digestive problems and heart issues, paediatrician Job van Woensel has told medical news website Medisch Contact.

But neither has tested positive for cornavirus despite a string of tests, Van Woensel said.

The World Health Organisation is currently researching if Covid-19 can cause rare and serious complications in children, after a number of cases were reported in Britain, soon followed by other EU countries and the US. According to some reports, up to 100 children may have been affected.

The symptoms are similar to a disease known as Kawasaki and to toxic shock, including high temperatures, a serious rash and flu-like complaints. Kawasaki is most common in children under the age of five.

The WHO has asked doctors throughout its network to be alert for the symptoms and a possible link with Covid-19.

‘If there is a connection,’ Van Woensel told Medisch Contact, ‘and it is still far too soon to suggest there is, then it may not come from the virus itself, but an over-reaction from the immune system.’ Similar cases had been reported before the epidemic, he told the magazine.

One reason why Covid-19 can be so serious is that it can trigger an extreme reaction in the immune system.

Karoly Illy, chairman of the Dutch association for child medicine, also said it is far too early to make a link with Covid-19. ‘There is currently no evidence,’ Illy told broadcaster NOS. ‘Some of the children with this illness have a Covid-19 infection and others, like the two in the Netherlands, do not.’