Severity of COVID-19 in Hospitalized Immunocompromised Children Across Canada

BACKGROUND: The association of immunocompromised states with pediatric COVID-19 outcomes remains unclear. This study assessed COVID-19 severity in hospitalized children with and without immunocompromising conditions. METHODS: Children <17 years hospitalized in Canada for COVID-19 (April 2020-December 2022) were identified through the Canadian Paediatric Surveillance Program and Canadian Immunization Monitoring Program, ACTive. Immunocompromised children (IC) were those with immune-compromising conditions and/or on immunosuppressive treatment. Severe COVID-19 was defined as intensive care unit admission, ventilator/hemodynamic support, organ complications or death. Adjusted risk ratios (aRR) for severe COVID-19 among IC versus nonimmunocompromised children (non-IC) were calculated using Poisson regression, adjusting for age, sex, other underlying conditions, SARS-CoV-2 lineage and vaccination. RESULTS: Among 3218 children hospitalized for COVID-19, 354 (11.0%) were IC. IC were older [median age 6.7 years (interquartile range = 3.6-11.8)] than non-IC [1.2 years (interquartile range = 0.2-4.8); P < 0.001]. IC experienced less respiratory distress than non-IC (20.9% vs. 48.1%). Severe COVID-19 (14.1% vs. 29.0%; P < 0.001), respiratory support (16.1% vs. 35.6%; P < 0.001) and intensive care unit admission (5.9% vs. 17.4%; P < 0.001) were less frequent in IC. IC were less likely to have severe COVID-19 than non-IC [aRR = 0.46 (95% confidence interval [CI]: 0.32-0.65)], with both immunodeficiency [aRR = 0.53 (95% CI: 0.39-0.73)] and immunosuppression [aRR = 0.40 (95% CI: 0.23-0.73)] subcategories independently associated with reduced risk. Compared to non-IC with other conditions, IC had a lower risk of severe COVID-19 [aRR = 0.35 (95% CI: 0.25-0.47)]. CONCLUSIONS: Hospitalized IC exhibited a lower risk of severe COVID-19 than non-IC, potentially reflecting lower admission thresholds for IC with respiratory infections.