The risk of reinfection with the Omicron coronavirus variant is more than five times higher and it has shown no sign of being milder than Delta, a study showed, as cases soar across Europe and threaten year-end festivities.

The results of the study by Imperial College London were based on UK Health Security Agency and National Health Service data on people who tested positive for Covid-19 in a PCR test in England between Nov 29 and Dec 11...