Omicron is more likely than other coronavirus variants to cause upper airway infection (UAI) among children, putting them at risk of heart attack and other severe complications, according to a study.

The researchers from the University of Colorado, Northwestern University, and Stony Brook University in the US analysed data from the National COVID Cohort Collaborative pertaining to 18,849 children under age 19 who were hospitalised with COVID-19.

The study, published last week in the journal JAMA Pediatrics, also found that Omicron causes UAI in younger children with the mean age of hospitalised children falling from about four years and five months during the pre-Omicron period to about two years and one month during the Omicron period. The researchers conducted the study to determine if cases of UAI among children increased when Omicron became the dominant SARS-CoV-2 variant in the US.

The proportion of children with a pediatric complex chronic condition was not significantly different in the pre-Omicron period compared with the Omicron period, they said. Overall, 21.1 per cent of children hospitalised with both COVID-19 and UAI developed severe diseases requiring measures like inserting a tube into the lungs to assist with breathing, known as intubation.

"Children with severe UAI are at risk of cardiac arrest from rapid-onset upper airway obstruction. They may require therapies typically provided in intensive care units, including frequent administration of nebulised racemic epinephrine, helium-oxygen mixtures, and intubation," the authors of the study noted. Nebulised racemic epinephrine is typically reserved for patients in the hospital setting with moderate-to-severe respiratory distress.

"While the rate of SARS-CoV-2 pediatric UAI is not overwhelmingly high, understanding this new clinical phenotype and the potential for acute upper airway obstruction may help guide therapeutic decision-making," they said. The Omicron strain of SARS-CoV-2 became dominant in the US the week ending December 25, 2021. The highly transmissible variant is known to cause lower severity disease than the Delta variant, the researchers noted.

This may be because Omicron replicates less efficiently in lung cells and more efficiently in the conducting airways, they said. The researchers acknowledged some limitations of this analysis, including that children who are still hospitalised are not represented in the study, and the frequency of severe disease observed in the Omicron period may be underestimated.