Long-Term Respiratory Outcomes in Pediatric Patients Following COVID-19 Infection and Multisystem Inflammatory Syndrome in Children (MIS-C)

Background/Objectives: Although SARS-CoV-2 infection is usually mild in children, some develop severe respiratory disease (RD) or multisystem inflammatory syndrome in children (MIS-C). We evaluated long-term respiratory symptoms, pulmonary function, and cardiopulmonary exercise performance in children recovering from SARS-CoV-2-related RD and MIS-C. Methods: This single-center prospective observational study included children hospitalized for SARS-CoV-2-related RD or MIS-C. Pulmonary function tests (PFTs) and cardiopulmonary exercise testing (CPET) were performed at a mean follow-up of 22.8 ± 9.8 months after hospitalization and compared between groups. Results: Forty-two children (25 RD, 17 MIS-C) were included. Persistent post-COVID symptoms were reported by 38.1% of participants and were more frequent in the RD group (56.0% vs. 11.8%; p < 0.01), with fatigue being the predominant symptom (p = 0.02). Pulmonary function and CPET parameters were comparable between groups, with no evidence of clinically significant ventilatory limitation or impaired aerobic capacity. VO2peak did not differ between groups. Multivariable regression identified the breathing reserve index and OUES normalized to body weight as strong positive predictors of aerobic capacity in both groups. Despite differences in follow-up duration, stratified analyses using a 24-month cut-off showed comparable physiological findings. Conclusions: Children demonstrated preserved pulmonary function and exercise capacity nearly two years after hospitalization for severe SARS-CoV-2-related RD or MIS-C. Despite these favorable objective findings, subjective symptoms persisted in a substantial subset of patients, particularly those recovering from RD, suggesting that symptom resolution may lag behind objective physiological recovery. OUES normalized to body weight and the breathing reserve index may serve as complementary markers of aerobic capacity.