Children are falling ill with a mystery "inflammatory syndrome" thought to be linked to coronavirus, senior doctors have warned.
NHS leaders have issued a nationwide alert after a sudden spike in children admitted to intensive care with rashes, kidney failure, and stomach problems.
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The young patients have been struck down by symptoms similar to toxic shock and Kawasaki syndrome, a rare condition that weakens the blood vessels and usually affects children under 5. Some have been admitted to intensive care after their hearts became dangerously inflamed, while others have been put on ventilators, it is understood.
On Monday night, Professor Stephen Powis, national medical director of NHS England, said he had asked experts to examine "as a matter of urgency" whether a coronavirus-related syndrome among children may be emerging in the UK.
"We have become aware in the last few days of reports of severe illness in children which might be a Kawasaki-like disease," he said. "Both Chris [Whitty] and I are aware of that, and we have asked our experts; I have asked the National Clinical Director for Children and Young People to look into this as a matter of urgency."
He said that Public Health England (PHE) was also looking into the reports, adding: "We're not sure at the moment - it is really too early to say whether there is a link."
Professor Chris Whitty, the chief medical officer, added: "This is a very rare situation but I think it is entirely plausible that this is caused by this virus, at least in some cases."
At Monday's Downing St press conference, Health Secretary Matt Hancock said he was "very worried" about the new wave of children going into intensive care.
NHS leaders were quick to reassure parents that only a "handful" of cases had been identified, and said the risk to children from coronavirus remained low. The link between the new combination of symptoms and Covid-19 has not yet been confirmed, they said, and the advice to parents remains unchanged.
In an alert sent to GPs, health chiefs said: "There is growing concern that a [Covid-19]-related inflammatory syndrome is emerging in children in the UK.
"Over the last three weeks, there has been an apparent rise in the number of children of all ages presenting with a multi-system inflammatory state requiring intensive care across London and also in other regions of the UK."
A similarly-worded warning was issued by the Paediatric Intensive Care Society to clinicians across the UK. It told clinical staff to urgently refer children suffering from three symptoms: abdominal pain, gastrointestinal symptoms, and cardiac inflammation.
It comes amid increasing pressure on the government to reopen schools, with some headteachers calling for classes to restart before the end of the summer term.
Since coronavirus first began to spread across the world last December, relatively few children have died from the disease. Only nine people under the age of 19 have died in England in hospital after testing positive for Covid-19, around 0.05 per cent of the total death toll. Their apparent resilience has puzzled doctors because young people are typically "super-spreaders" of other viral illnesses such as influenza.
Children began presenting with the new syndrome around three weeks ago, according to the NHS alert. Often the patients are found to be suffering from stomach pain and gastrointestinal symptoms including vomiting and diarrhoea. Unlike adults, however, most of the children do not initially present with a cough or other respiratory problems, it is understood. The majority are found to have a fever and a persistently high temperature.
One paediatric doctor at a major London hospital told the Telegraph that some of the children have developed "darkened knuckles" for reasons currently unknown. Medics at the hospital are currently treating around a dozen children aged mostly between 10 and 12, the doctor said.
"We're baffled by this," he said.
"These children are becoming unwell quite quickly. They start feeling generally unwell, with non-specific symptoms.
"Then many of them develop rashes on the neck, forearms and abdomen. The rashes can be flat, raised, angry-looking or gentle. No patient is exactly the same.
"Some come in with darkened knuckles, which is not normal. It suggests some form of vasculitis - inflammation of the blood vessels. It's likely to be some form of auto-immune reaction or ischemic response, where the blood supply is restricted.
"It's all very new. We don't know if there's a mutated form of the virus that is causing this.
"The timeline is odd, too. All the kids I have talked to have stayed inside for the last few weeks, so it doesn't match what we know about the incubation period. But because of the lack of testing, we can't know for sure if they caught it off their parents, or by some other route.
"They can then become seriously ill very quickly. Some of the kids I treated have been transferred to intensive care because their organs were starting to fail. None of them have yet died, as far as I'm aware."
All 12 children in the London hospital tested positive for Covid-19, although in other areas some patients have tested negative. A number have been taken into intensive care with inflammation of the heart.
Other leading paediatricians confirmed that they too had seen a sudden rise in cases. It is not known whether any of the children have yet died.
Sir Jeremy Farrar, director of the Wellcome Trust and a member of the Government's Scientific Advisory Group for Emergencies (Sage), said the alert was "really important" and called for the warning to be circulated widely to hospitals across the country.
Meanwhile, doctors in other countries reported similar cases in their hospitals. A general inflammatory syndrome was reported for selected Covid-19 patients recently in University Hospital Zurich, while an Italian study published on Monday reported a "significant increase of Kawasaki disease in Covid positive children".
In the US, leaders at the Children's National Hospital in Washington said they had been "surprised" by the number of children needing critical care.
Kawasaki disease affects mostly children under 5 and causes inflammation in the walls of the blood vessels. The rare condition can lead to aneurysms, heart attacks or heart failure.
Symptoms include a fever, a rash, swollen hands and feet, redness in the whites of the eyes and swollen lymph glands in the throat.
Experts cautioned that the UK alert was a standard way of raising awareness quickly among clinicians about potential new illnesses, rather than confirmed evidence of a new syndrome. PHE announced on Monday that every case of coronavirus in children will be analysed by central labs.
Professor Adilia Warris, paediatric infectious diseases specialist at the University of Exeter, said: "As we don't know yet the full range of clinical presentations caused by Covid-19, we keep every possibility open that clinical presentations that can't be explained by other causes might be caused by Covid-19, or even a not yet recognised pathogen.
"Please do consider that the absolute number of those cases are very low [a handful at the moment].
"The call to ask if other colleagues have had comparable experiences over the last week is so we are able to define what is going on, and if there is reason for additional assessment into this."
Professor Simon Kenny, NHS national clinical director for children and young people, said: "Thankfully Kawasaki-like diseases are very rare, as currently are serious complications in children related to Covid-19, but it is important that clinicians are made aware of any potential emerging links so that they are able to give children and young people the right care fast.
"The advice to parents remains the same: if you are worried about your child for whatever reason, contact NHS 111 or your family doctor for urgent advice, or 999 in an emergency, and if a professional tells you to go to hospital, please go to hospital."