Rationale and approach

•  In children and young people, the post-coronavirus disease 2019 (COVID-19) condition, also known as long COVID, is associated with a range of persistent symptoms following infection with severe acute respiratory syndrome coronavirus 2.

•   Research on post-COVID-19 condition varies in outcomes studied. A consensus on a minimum set of essential outcomes, referred to as a core outcome set (COS) is needed for better data comparison in children and young people.

•   There is also an urgent need for decisions to be made on which measurement instruments are the most appropriate for assessing these core outcomes, in order to develop a core outcome measurement set (COMS), to optimise data comparability and synthesis.

•   To develop the COS, we conducted a study that included a literature review, a two-round online Delphi process with >214 participants from 37 countries, with over half of them being parents of children with post-COVID-19 condition and children and young people, and an online consensus meeting. The Delphi process included rating 25 different outcomes.

•   For the development of COMS, we then performed an expert online modified Delphi process and an online consensus workshop to discuss and then vote anonymously on measurement instruments.

Findings

•   In the field of paediatric care, it is recommended that the following outcomes to be consistently measured in research and clinical practice when assessing post-COVID-19 condition: fatigue; post-exertion symptoms; alterations in studies, work or occupational activities; as well as functional changes, symptoms and conditions relating to cardiovascular, neurocognitive, gastrointestinal and physical health.

•   Instruments for measurement of fatigue, gastrointestinal, neurocognitive outcomes and physical functioning were recommended for use in research and clinical practice for children and young people with post-COVID-19 condition. For the three other core outcomes, the most favoured measurement instruments identified from this consensus procedure have been documented, even though no individual measurement instrument met a priori criteria for consensus.

Future directions and implications

•   To enhance our understanding of post-COVID-19 condition in children, there is a need for further standardisation of clinical and research practices using the identified core outcomes and associated measurement instruments.

•   Future research should focus on refining and validating the measurement instruments that were favoured but did not achieve consensus among participants.

•   Incorporating the lived experiences and perspectives of children and young people affected by post-COVID-19 condition as well as their carers is crucial for future research, including instrument development and improvements to patient care.

•   Agreed measurement instruments should be considered in future work and insights from this research should guide policymakers in creating initiatives that address the effects of post-COVID-19 condition on children and young people in both healthcare and research environments.