They also cautioned that their data were gathered during an early stage of the Omicron wave, when the overall infection rate was quite low. Infected people with relatively mild symptoms might have been more likely to be admitted to hospitals back then, before the wards filled up.

In Scotland, researchers examined Delta and Omicron cases in November and December, looking at how many patients with each variant were admitted to a hospital. Omicron infections are associated with a two-thirds reduction in the risk of hospitalization compared with the Delta variant, the researchers found.

Mark Woolhouse, a professor of infectious diseases at the University of Edinburgh and a co-author of the new study, said that the dramatic surge of Omicron meant that even if these preliminary results held up, the variant would still put a lot of people into hospitals very quickly.