Severe outcomes in unvaccinated COVID-19 cases <18 years during different variant waves in Norway
Abstract
Objectives
We used linked individual-level data from national registries to compare the risk of severe outcomes among unvaccinated COVID-19 cases <18 years between waves of the SARS-CoV-2 Alpha, Delta and Omicron variants in Norway.
Methods
Our outcomes were hospitalisation with acute COVID-19 or multisystem inflammatory syndrome in children (MIS-C). We calculated adjusted risk ratios (aRR) with 95% confidence intervals (CIs) using multivariable log-binomial regression, adjusting for variant wave, demographic characteristics and underlying comorbidities.
Results
We included 10,538 Alpha (21 hospitalised with acute COVID-19, 7 MIS-C), 42,362 Delta (28 acute COVID-19, 14 MIS-C) and 82,907 Omicron wave cases (48 acute COVID-19, 7 MIS-C). The risk of hospitalisation with acute COVID-19 in cases <1 year was lower in the Delta (aRR: 0.28, 95% CI: 0.16–0.89) and Omicron wave (aRR: 0.41, 95% CI: 0.20–0.81), compared to the Alpha wave. We found no difference in the risk for this outcome for Omicron compared to Delta in any age group. The risk of MIS-C was lower in the Omicron wave compared to the Alpha (aRR: 0.09, 95% CI: 0.03–0.27) and Delta wave (aRR: 0.26, 95% CI: 0.10–0.63).
Conclusions
We found no evidence of a difference in the risk of hospitalisation due to acute COVID-19 among unvaccinated cases <18 years for Omicron compared to Delta, but a reduced risk among cases <1 year in Omicron and Delta waves, compared to Alpha. Results also suggest a decrease in the risk of MIS-C in the Omicron wave compared to the Alpha and Delta waves.
Article Summary
We compare the risk of severe outcomes in unvaccinated COVID-19 cases <18 years between waves of the SARS-CoV-2 Alpha, Delta and Omicron variant in Norway.
What’s Known on This Subject
Currently, limited evidence suggests no clear difference in the risk of severe disease outcomes among children infected with different SARS-CoV-2 variants. The risk of multisystem inflammatory syndrome in children following infection with the Omicron variant has not been quantified.
What This Study Adds
We find a lower risk of hospitalisation due to acute COVID-19 among cases <1 year in the Delta and Omicron waves compared to the Alpha wave, and a lower risk of multisystem inflammatory syndrome in the Omicron wave, in Norway.
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