Background Further studies are needed to understand the underlying mechanism of Long-COVID (LC) symptoms in children.

Aim To investigate whether LC in children was associated with a lower lung function and an impaired lung ultrasound (LUS).

Methods We carried out a prospective study including 58 children aged 5-17 years: 28 with LC compared to 30 asymptomatic children with previous COVID-19. After a median period of 4.5 months (1-95% range 2-21) from the infection, lung function was assessed by spirometry, body plethysmography, diffusion lung capacity for carbon monoxide. Airways inflammation was investigated by fractional exhaled nitric oxide (FeNO). LUS was performed independently by two experienced clinicians.

Results We found that children with LC were older than controls (mean (SD) 12(4.1) vs 9.7(2.6); p=0.04). Children with LC complained more frequently fatigue (46.4%), cough (17.9%), exercise intolerance (14.3%) and dyspnoea (14.3%). Lung function was normal in both groups. The frequency of LUS abnormalities was similar between the two groups (43.3% children with LC vs. 56.7% controls; p=0.436). Children with LC showed lower FeNO values ((log difference -0.30 (CI 95% -0.50, -0.10)), but no association of LC with a lower lung function and abnormal LUS findings was found.

Conclusions Lung functional and structural abnormalities were not different between children with LC and asymptomatic subjects with previous COVID-19. In addition, patients with LC showed lower FeNO values than controls, suggesting its potential role as a marker in LC. However, further larger studies are needed to confirm our findings.