The research, based on UK infection data, casts doubt on the hopes of some experts that a change in the virulence of the new variant would ease the pressure on health systems despite Omicron’s high levels of infectiousness.

“The study finds no evidence of Omicron having lower severity than Delta, judged by either the proportion of people testing positive who report symptoms, or by the proportion of cases seeking hospital care after infection,” said the research team, led by Professor Neil Ferguson, an infectious disease modeller and government science adviser.

However, they cautioned that hospitalisation data “remains very limited at this time”. The study said data suggested “at most, limited changes in severity compared with Delta”…

Addressing the question of severity, an analysis of 120,000 Delta cases and 15,000 suspected Omicron cases found that people infected with Omicron were no more likely to be asymptomatic than those infected with Delta.