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New definitions for long COVID developed with patients and carers

Published: 08 February 2022

Researchers have developed new definitions for what long COVID is and the key effects in children and adults, which will help harmonise research and improve understanding of the condition.

The Non-hospitalised Children and young people with Long Covid (CLoCk) study, funded by NIHR and UK Research and Innovation, has for the first time defined long COVID in children. The Post-COVID Condition Core Outcomes (PC-COS) study, also funded by NIHR, has defined the key ‘health outcomes’ that should be measured as a minimum in long COVID research in adults.

The two NIHR-funded research groups worked with patients and carers to develop their definitions, using a democratic technique called the Delphi consensus process. This process involves whittling down statements through several rounds of discussion, with the opinions of every participant accorded equal importance.

These new definitions will ensure that research is directed towards elements of long COVID that are most important to patients and will help researchers to reliably compare and evaluate studies on prevalence, disease course and outcomes, providing a more accurate picture on the true impact of long COVID.

A diverse condition affecting thousands

The World Health Organisation defines post COVID-19 condition, or ‘long COVID’, in adults as occurring in people with a history of probable or confirmed SARS-CoV-2 infection, usually 3 months from the onset of COVID-19, and with symptoms that last for at least 2 months and cannot be explained by an alternative diagnosis. Until now, no such definition existed for long COVID in children.

Common symptoms of long COVID include fatigue, shortness of breath, cognitive dysfunction but also others, and generally have an impact on everyday functioning. More than 200 symptoms have been associated with long COVID to date.

An estimated 3% to 12% of people infected with coronavirus have symptoms 12 weeks after the initial infection. Prevalence estimates for long COVID specifically in children and young people vary from 1%-51%, with the CLoCk study estimating that up to 14% experience ongoing symptoms.

Defining long COVID in children and young people

The CLoCk researchers worked with a panel of more than 100 researchers, experts in health service delivery, and children with long COVID and their parents to score 49 statements on long COVID. These statements were then reviewed by a panel of eight 11-17 year olds affected by long COVID to reach final agreement.

Their definition of long COVID is a condition in which a child or young person has symptoms (at least one of which is a physical symptom) that:

  • Have continued or developed after a diagnosis of COVID-19 (confirmed with one or more positive COVID tests)
  • Impact their physical, mental or social wellbeing
  • Are interfering with some aspect of daily living (eg, school, work, home or relationships) and
  • 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 definition, published in the journal of Archives of Disease in Childhood, closely complements the WHO definition for long COVID in adults.

Professor Sir Terence Stephenson, Nuffield Professor of Child Health at UCL Great Ormond Street Institute of Child Health and Honorary Consultant Paediatrician University College Hospital & Great Ormond Street Hospital, said: “This research definition will allow us to compare research from different countries and will reduce the variability in prevalence estimates of long COVID.”

The researchers emphasise the need to differentiate between a clinical case definition and a research definition of long COVID. “It is understandable that the patient groups representing people with long COVID are concerned that a definition could restrict access to services,” said Prof Stephenson. “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 process of arriving at this definition also took into account quantitative data from the CLoCk study, an innovation within the Delphi approach process. These data have now been published as a peer reviewed paper in Lancet Child and Adolescent Health.

Deciding on the key health outcomes in long COVID

The PC-COS researchers worked with more than 1,000 clinicians, researchers, patients and carers in 71 countries to develop a core outcome set for long COVID in adults. A core outcome set is an agreed-upon minimum set of outcomes that should be measured and reported in all studies in a specific field.

The core outcomes for long COVID in adults, available as a pre-print, are:

  • fatigue or exhaustion
  • pain
  • post-exertion symptoms
  • work/occupational and study changes
  • survival
  • ‘functioning, symptoms and conditions’ for each of the following outcomes:
    • cardiovascular
    • respiratory
    • nervous system
    • cognition
    • mental
    • physical

A ‘recovery’ outcome was added from a previously published core outcome set on COVID-19.

Dr Daniel Munblit, Honorary Senior Lecturer at Imperial College London and Professor at Sechenov University, Russia, said: “These core outcomes are the necessary minimum outcomes that should be measured in studies, to help standardise and harmonise data collection and research worldwide. However, this does not mean that other outcomes are not important.”

Dr Timothy Nicholson, Clinical Senior Lecturer at King's College London, added: “Long COVID is a new disease in terms of the heterogeneity and complexity of what we’re seeing, with multiple symptoms across many domains, so it’s a really complicated condition medically to grapple with.

“If everyone is measuring different things, it’s very hard to collate that information and compare it. What we’re doing with these core outcomes is creating one of the planks that allows building of the evidence base to inform our understanding of long COVID.”

Part of a diverse portfolio of long COVID research

These two studies form part of a diverse portfolio of long COVID research that have received nearly £40 million investment from the NIHR.

The funded research ranges from characterising the disease and understanding who it affects, through to diagnosis and also treatment, rehabilitation and recovery.

This extensive portfolio of research is already answering important questions about long COVID, such as recent research that used a novel imaging technique to identify abnormalities in the lungs of long COVID patients with breathlessness but whose other tests are normal.

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