For every 100,000 unvaccinated children in the age group, 19.1 per were hospitalised with Covid-19 between mid-December and late February, compared with 9.2 per 100,000 vaccinated kids, the US Centers for Disease Control and Prevention reported.

The researchers looked at nearly 400 hospitalisations in 14 states during the period.

It found that among the 397 children who were hospitalised with Covid when Omicron was dominant, 87% were unvaccinated, one third had no underlying medical conditions, and 19% were admitted to an intensive care unit.

The highly contagious Omicron variant, which drove coronavirus infections to record levels in the United States in January, fueled an increase in Covid-19 hospitalisations among those under age 18, leading to concerns about the impact on unvaccinated children.

US regulators had authorized the Pfizer PFE.N/BioNTech 22UAy.DE Covid-19 vaccine for children aged 5 to 11 years in October, prior to the Omicron surge.

Just 28% of children in the age group – around 8 million – are fully vaccinated, according to CDC data.

The study also found that peak Covid-19 hospitalisation rates among children in the age group were higher during the Omicron wave than when Delta was the predominant variant.

(Reporting by Amruta Khandekar in Bengaluru; Editing by Bill Berkrot)