Incidence of severe and non-severe SARS-CoV-2 infections in children and adolescents: a population-based cohort study using six healthcare databases from Italy, Spain, and Norway.

We aim to estimate the incidence rates (IRs) of SARS-CoV-2 infections stratified by disease severity and comorbidities in pediatric population and to describe the COVID-19 vaccination coverage in children with and without comorbidities. A population-based cohort study was conducted in 6 electronic healthcare records databases from Italy, Spain, and Norway. The study lasted from 1 January 2020 to the latest databases' available data in each site, i.e., in Italian ARS Tuscany and PEDIANET: December 2021, in Spanish BIFAP: February 2022; SIDIAP: June 2022, and VID: December 2021. Finally, in Norwegian Health Registries: December 2021. Children and adolescents were included and stratified into three age categories (< 5, 5- < 12, and 12- < 18 years old). IRs (95% confidence intervals) per 100 person-years (PY) for non-severe (positive SARS-CoV-2 test or diagnosis without hospitalization) and severe COVID-19 (hospitalization, intensive care unit admission, and death after COVID-19) are reported. The cumulative COVID-19 vaccination rollout was stratified by population with and without comorbidities. The study population comprised 5,654,040 individuals < 18 years of age (51% females) across the six European databases (median age: 6 years), with 1.4 to 8.5% of them having at least one at-risk comorbidity for severe COVID-19. Incidence rates of severe COVID-19 were low (0-1 per 100 PY) but 3 to 4 times higher among children and adolescents with comorbidities during Omicron BA.1-2 wave in December 2021-January 2022. Percentages of vaccination rollout in the general population were between 13% in PEDIANET-IT and 64% in BIFAP-ICU-ES. In ARS-IT and SIDIAP-IT, vaccination rate in children with comorbidities was slightly lower than that in the general population.

Conclusion: Severe COVID-19 was rare across databases, but up to 3 to 4 times higher in children with comorbidities during the predominance of Omicron BA.1-2 variant in winter 2021-2022. COVID-19 vaccination coverage was slightly lower in children with comorbidities in ARS (Tuscany) and SIDIAP (Catalonia) data sources. Our findings will inform future public policies aimed to protect the pediatric population, both within these countries and globally.

What is known: • Pediatric population is susceptible to SARS-CoV-2 infection. • COVID-19 severity rates in children vary across study settings and context.

What is new: • This study confirms the low severity rates of COVID-19 in the pediatric population based on a large cohort of children and adolescents residing in Spain, Italy, and Norway. • Incidence of severe COVID-19 in children and adolescents with comorbidities was up to 3 to 4 times higher than in the general pediatric population during the SARS-CoV-2 high transmission wave of Omicron BA.1-2 variant in winter 2021-2022 in Italy and Spain.