Children and young people have less severe Covid-19 than adults and death is exceptionally rare, new study confirms.

Researchers from the universities of Edinburgh and Liverpool, Imperial College London and the Royal Hospital for Children in Glasgow identified only six Covid deaths among children and young people aged under 19 across hospitals in Scotland, England and Wales by mid-July this year.

This puts the Covid mortality rate for hospital admissions in this age group at a "strikingly low" one per cent, note the authors, compared with 27% across all ages admitted to hospital over the same time period.

Three of the deaths were in newborn infants aged less than 28 days who were at particularly high risk due to being very premature, born with a complex heart abnormality, or having developed bacterial sepsis.

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There were also three Covid deaths in teenagers aged 15 to 18. One was immunosuppressed as a result of chemotherapy for cancer and had also contracted bacterial sepsis, while the other two deaths were in adolescents with profound learning disability and pre-existing respiratory problems.

In total researchers identified 651 inpatients under-19s confirmed to have Covid-19 through either an antigen or antibody test across 138 hospitals in Britain between January and July.

They included 55 patients who appeared to have contracted the virus while in hospital.

Outcome data was available for 627 of these children and young people.

Dr Olivia Swann, lead author and expert in paediatric infectious diseases at Edinburgh University, said: “Researchers often want to call attention to large numbers of patients in their studies, however, we want to highlight that children made up only a fraction of a percent of all Covid-19 admissions across the UK in our study and that severe disease was rare.”

Being of black ethnicity was "significantly associated with admission to critical care", echoing patterns seen among adult Covid patients in Britain.

Overall, 18% of children and young people in hospital with Covid were admitted to intensive care.

READ MORE: Hospital admissions for chest pain halved in first month of lockdown 

Children aged less than one month old or between 10 and 14 were also more likely to require critical care, and being premature, obese, or having respiratory or heart conditions also increased the risk of intensive care admission.

Children admitted to critical care were also more likely to have presented with rarer Covid complications including diarrhoea, conjunctivitis, and altered consciousness or confusion.

However, this was only the case in a sub-group of patients identified as meeting the World Health Organization criteria for multisystem inflammatory syndrome (MIS-C) - a rare condition thought to be linked to Covid-19.

The condition was first described in May 2020 among a cluster of children admitted to critical care units in London, but also reported among youngsters in France and Italy.

It is characterised by an excessive and damaging immune response similar to toxic shock syndrome or Kawasaki disease, which causes blood vessels to swell - most commonly in children under five.

READ MORE: Why the surge in demand for testing was predictable after schools reopened 

Researchers identified 52 cases of children with MIS-C among the admissions and found that while they were five times more likely to be admitted to critical care than non-MIS-C patients, none had died.

MIS-C was also more common among non-white youngsters and older children. The median age was 10.7 compared to 4.5 for overall admissions among children and teenagers.

These children were also more likely to show symptoms such as fatigue, headache, muscle pain and sore throat, and have a low blood platelet count.

Researchers are calling for the WHO’s definition of MIS-C to be updated to help doctors identify more children with the condition and improve their treatment.

The findings, published today in the British Medical Journal, provide the largest and most detailed description in the world to date of Covid-19 and MIS-C in children and young people.

Dr Louisa Pollock, consultant in paediatric infectious disease at the Royal Hospital for Children in Glasgow, said: “Parents should be reassured by this study which confirms very few children were seriously affected by Covid-19.

"As children return to school, and over the winter months, it is important we continue to monitor Covid-19 in children.”

Professor Fiona Watt, chief executive of the Medical Research Council, said: “This is a significant study involving 138 hospitals across England, Wales and Scotland showing that children and teenagers are less likely than adults to develop severe Covid-19 or die from the disease.

"Indeed, the findings suggest it is rare for young people to end up in hospital with Covid-19.

“However, while the overall the risk for young people is lower, the added risks of obesity and ethnicity are shared with adults. We need to understand this, and also why a very small number of children are suffering from an inflammatory syndrome.

"Obviously the goal is to ensure that everyone who develops Covid-19 has the most appropriate treatment.”