A DEFINITION of 'Long Covid' in children has been formally agreed for the first time by a panel of international experts. 

The landmark paper accepted for publication today in the BMJ journal, Archives of Disease in Childhood, sets out a list of five criteria which include continuing to experience symptoms - one of which must be physical - 12 weeks or longer after a positive Covid test. 

A consistent definition - widely applied - is seen by researchers as a key step towards strengthening the evidence base for the debilitating condition. 

Currently, the "inconsistent" range of definitions in use around the world - which vary by number, type and duration of symptoms - has led to the prevalence of Long Covid in children being estimated as anything from one per cent to 51%.

It also remains "unclear whether Long Covid represents one or many different conditions", state the authors - led by scientists at University College London. 

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The paper adds: "Research into the prevalence and impact of Long Covid has consequently been hampered, thereby delaying the implementation of policies and services that could help affected [children and young people]."

A consistently applied definition of Long Covid is necessary to reliably compare and evaluate studies on prevalence, disease course, and outcomes, providing a more accurate picture on the true impact of the condition, say the authors.

A consensus was reached among a representative panel of 120 international experts skilled in service delivery (47), research (50), and lived experience (23), after careful scrutiny of 49 statements each of which was scored from 1-9, depending on their perceived importance.

Following input froma panel of eight 11-17 year olds affected by Long Covid, the condition in under-18s was defined as: 

  • A condition in which a child or young person has symptoms (at least one of which is a physical symptom
  • These symptom(s) have continued or developed after a diagnosis of Covid-19, confirmed through one or more positive Covid tests
  • The symptom(s) impact on physical, mental or social wellbeing
  • They interfere with some aspect of daily living such school, work, home or relationships
  • The symptom(s) persist for a minimum duration of 12 weeks after initial testing for Covid-19 (even if symptoms have waxed and waned over that period

The researchers summarise their definition as: "Post-Covid-19 condition occurs in young people with a history of confirmed SARS CoV-2 infection [the virus responsible for COVID-19 infection], with at least one persisting physical symptom for a minimum duration of 12 weeks after initial testing that cannot be explained by an alternative diagnosis.

"The symptoms have an impact on everyday functioning, may continue or develop after Covid-19 infection, and may fluctuate or relapse over time.”

Their definition closely overlaps with that proposed by the World Health Organisation (WHO) for Long Covid in adults.

The researchers note that emerging data "indicate that there are similarities with the adult symptoms but also differences, for example in the higher proportion of [children and young people] who present without symptoms at the time of their initial infection". 

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They note that acute Covid infection in children and young people "is usually asymptomatic or mild compared to adults", and that children are more likely overall than adults to make a full recovery without any lingering illness.

Over 200 symptoms have been associated with Long Covid in adults but the most common symptoms in both adults and children are similar - particularly fatigue and headache.

A UK survey of self-reported Long Covid in 320,825 people reported a prevalence of 0·16% for those aged two to 112-11 years, rising to 0·65% for 12-16 years, and 1·22% for 17-24 years.

However, a large national study of Long Covid in children - the CLoCk study - found that at three months on from a positive Covid test, 66.5% of children and young people with a positive test, and 53.3% of those with a negative test (potentially indicating cold-like symptoms caused by a different virus) still had symptoms, at least one of which was physical.

In addition, 30.3% and 16.2%, respectively, still had three or more symptoms. 

The researchers emphasise that their "research definition" of Long Covid should not be used to restrict access to clinical care, however. 

They state: “It is understandable that the patient groups representing people with Long Covid are concerned about a definition that could restrict access to services that are needed.

"In our view, the decision whether a child or young person can see a healthcare professional, access any support needed, or be referred, investigated or treated for Long Covid should be a shared decision involving the young person, their carers and clinicians.

"The stringent research definition arrived at through this consensus process and the definition aligned to that of the WHO can be used to inform that decision making process, however, it should not be used as the yardstick by which it is determined if [children and young people] can access care."