The highly-mutated strain was labeled a "variant of concern" late in November by the World Health Organization and was soon spreading across the world.
"The Omicron VOC is likely to become the dominant variant in the EU/EEA within the first two months of 2022," a ECDC rapid risk assessment read.
The ECDC said it did not have enough data to assess the severity of the disease caused by Omicron, but if it is equal to or weaker than that of Delta, its increased transmissibility would cause an exponential growth of cases that would rapidly outweigh any benefits of a potentially reduced severity.
European Health Commissioner Stella Kyriakides tweeted that Europeans "cannot throw caution to the wind" as they prepare for the festive winter season.