Introduction::
This study aimed to assess and compare the long-term non-cardiac complications of the multisystem inflammatory syndrome in children (MIS-C) triggered by consecutive variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Material and methods::
Multisystem inflammatory syndrome in paediatric patients was assessed in the paediatric office at 4–12 and 12–24 weeks and then by a telephone survey at least 24 weeks after hospitalisation. During each follow-up, we obtained information regarding the prevalence of long-COVID symptoms, body mass index, COVID status, need for rehospitalisations, and any consultations with specialists. Additionally, we assessed the participant’s quality of life (QoL) using the KIDSCREEN-10 questionnaire over the phone.

Results::
A total of 116 patients with MIS-C (74 during Original/Alpha, 27 during Delta, and 15 during Omicron variant surges) admitted to the Children’s Hospital of Krakow between 1 November 2020 – 5 May 2023 were included in the analysis. Regardless of the follow-up period, the frequency and variation of most symptoms did not differ significantly between groups. The only difference was a higher frequency of fatiguability/weakness in the Original/Alpha group, during the 4–12-week follow-up (37.9% vs. 10.5% vs. 9.1%; p = 0.03). The multivariable regression revealed older age (OR = 1.13, 95% CI: 1.01–1.26, p = 0.03), but not the particular variant, as an independent factor for long-COVID. Additionally, the results of long-term follow-up (more than 24 weeks) showed above-average KIDSCREEN-10 scores despite a high incidence of long-COVID symptoms.

Conclusions::
The impact of individual SARS-CoV-2 variants appears to be less important on the onset of long-COVID symptoms than other factors, such as age. Long-term follow-up indicated an overdiagnosis of non-specific long-COVID symptoms, in the case that the QoL after MIS-C was non-inferior to the general paediatric population.