Clinical severity of Omicron and Delta SARS-CoV-2 infections in children

Background: We aimed to compare the clinical features and severity of the Omicron and Delta variant infections among children hospitalized for coronavirus disease 2019 (COVID-19).

Methods: Children 12 years old or less hospitalized for COVID-19 across five hospitals between January 1, 2021 and March 31, 2022 were identified using the state's pediatric COVID-19 registry. Delta and Omicron-infected patients without previous COVID-19 infection, COVID-19 vaccination, or co-infections were propensity-score matched 1:1 to control for differences in baseline characteristics. Clinical manifestations, treatments, and outcomes were analyzed. Disease severity was assessed using an adapted WHO ordinal scale.

Results: Of the initial 1367 patients, 668 had Delta infection and 699 had Omicron infection. Propensity-score matching produced 558 matched pairs. Patients with Omicron infection were more likely to present with croup (the odds ratio, OR, was 10.87, with a 95% confidence interval, CI, ranging from 2.54 to 46.59), lower respiratory tract infection (OR 2.32, 95% CI, 1.48-3.64) and seizures (OR 8.39, 95% CI, 5.04-13.99) compared with those with Delta infection. Omicron was associated with increased odds of moderate/severe disease (OR 6.14, 95% CI, 4.72-7.99) and a greater need for intravenous fluid therapy (OR 6.00, 95% CI, 4.29-8.39), corticosteroids (OR 3.08, 95% CI, 1.66-5.72), empirical antibiotics (OR 1.70, 95% CI, 1.10-2.64), and low-flow nasal oxygen therapy (OR 3.68, 95% CI, 2.17-6.22) in comparison with Delta.

Conclusion: Children hospitalized with Omicron infection demonstrated a distinct clinical profile compared to those with Delta infection, with increased likelihood of moderate/severe disease and higher utilization of health-care resources.