LONDON — The World Health Organization is “urgently” investigating a potential link between the coronavirus and Kawasaki syndrome, an illness of unknown cause that primarily affects children under 5.

“We are aware of this newly described syndrome from a number of countries in Europe and potentially a small number of cases in North America,” Dr. Adam Finn, chair of the WHO's European Technical Advisory Group, told a news briefing Thursday.

“We are urgently conducting a surveillance study in the United Kingdom to establish what is going on,” he added.

Also known as Kawasaki disease, on its website the Centers for Disease Control and Prevention describes Kawasaki syndrome as “acute febrile illness of unknown cause" that "primarily affects children younger than five years of age.”

Clinical signs include “fever, rash, swelling of the hands and feet, irritation and redness of the whites of the eyes, swollen lymph glands in the neck, and irritation and inflammation of the mouth, lips, and throat,” it adds.

Finn said the WHO was aware that around 20 cases had been reported in London and elsewhere in the U.K., adding that other places were also reporting cases.

“Only around half these children are testing positive for coronavirus so at this point we are not completely clear as to the causal relationship although this may be a late complication of the infection with a hyperinflammatory syndrome of some kind,” he said.

“The size and the exact nature of this problem is only beginning to emerge, and we will learn a lot more in the coming days and weeks,” he added.

Finn also cautioned that it could be some time before a COVID-19 vaccine became available.

“As in a horse race, the first horse out of the box is not necessarily the horse that finishes the race and here, we’re not so much interested in the winner as how many horses we can get to the finishing line,” he said.

“Vaccines that are already in trials might be the ones attracting the most attention and most optimism," he said, adding that we have to bear in mind "that they may prove not to be safe and they may prove not to be effective and, perhaps most importantly of all, they may not prove to be the ones that can most easily be manufactured and distributed effectively."