Background

SARS-CoV-2 variants have an impact on the outcome of infection in adults. However, their influence on COVID-19 in children is still insufficiently studied. We aimed to describe the outcome of COVID-19 in children during the original, Alpha, Delta, Omicron BA.1/BA.2 and BA.4/BA.5 variant periods.

Methods

Demographic and disease-related data of all patients aged <19 years with SARS-CoV-2 positivity or COVID-19 diagnosis (ICD-10 codes U07.1, U07.2) between 27/Feb/2020 and 01/Mar/2023 were extracted from the Estonian Health and Welfare Centre’s database. Only the first episode per patient per variant period  (including reinfections) was included in the study.  A genotype-based COVID-19 wave was defined as a period when 50% of the genotyped samples belonged to the respective genotype. Outcome measures included hospitalization, intensive care admission, diagnosis of MIS-C, incidence of long-COVID and type 1 diabetes (T1D). Statistical analysis was performed using Fisher’s exact test. This work is part of the VERDI project (101045989), funded by the European Union. 

Results

Altogether 145 922 cases of COVID-19 in 127 277 children (51.2% male; median 10 yo) were detected. The incidence of COVID-19 was the highest during Omicron BA.1/BA.2 period (Table1). The rate of hospitalization due to COVID-19 was significantly greater during Omicron BA.1/BA.2 and BA.4/BA.5 periods, long-COVID was more frequent during Omicron BA.1/BA.2 period. The incidence of newly diagnosed T1D, adjusted to person-years, was similar in all periods. The T1D incidence increased from 35.1/100 000 in 2017-2019 to 52/100 000 in 2022 (p<0.01). 

Conclusions    

Similarly to adults the outcome of SARS-CoV-2 infections changed during the pandemic. The rise in the hospitalization rate and incidence of long-COVID during Omicron BA.1/BA.2 period was due to the greater incidence of SARS-Co-2 in children rather than increased severity.