Paediatric post-COVID condition, different faces of a new disease

At the beginning of the COVID-19 pandemic we were confronted with Paediatric Post-COVID Condition (PPCC). This thesis describes our first insights into this new phenomenon. Our first study focused on children hospitalized for acute COVID-19 or MIS-C, in which pulmonary sequelae did occur frequently four to twelve months after hospital admission. It showed that CPET testing is frequently abnormal and helpful to provide insights into pathophysiology of sequelae. In the beginning of the COVID-19 pandemic PPCC was still an unknown entity. We described the experience of Dutch paediatricians with PPCC end of 2020 and demonstrated both the high burden of disease, and the need to both organize care and research focusing on PPCC. To inform organization of care, we first investigated the prevalence of PPCC in a Dutch low and high risk setting, compared to a negatively tested group. PPCC prevalence was respectively 14.6, 29.2 and 2.3% three months after acute infection, and did decrease over time. Children with PPCC had lower physical health-related quality of scores and higher fatigue scores. Definitions used clearly influence PPCC prevalence, demonstrating the importance of data harmonization tools. Second, we examined international care PPCC care programs and their patients, and highlighted the broad symptomatology of PPCC, and heterogeneous diagnostic and therapeutic approach. The International Post-COVID-Condition in Children Collaboration (IP4C) published an overview of priorities to accelerate and improve PPCC care. These combined findings demonstrate the urgent need for further scientific substantiation of PPCC care programs to improve PPCC outcomes.