STOCKHOLM - A rapid increase in the number of Omicron COVID-19 variant cases is imminent, the European Centre for Disease Prevention and Control (ECDC) warned on Wednesday.

The European Union's (EU) health watchdog also urged countries to rapidly intensify their vaccination efforts, and reintroduce and strengthen other measures to slow down the spread of the virus.

By Wednesday, 2,629 Omicron cases had been confirmed in 27 countries in the EU and the European Economic Area (EEA), 502 of these in the past 24 hours.

This indicates that community transmission is already ongoing in the EU and EEA countries, the ECDC said. Based on modeling predictions, a further rapid increase is imminent, ECDC Director Andrea Ammon said.

"We assess the probability of further spread of the Omicron variant in the EU/EEA as very high, and it is considered very likely to cause additional hospitalizations and fatalities, further to those already expected from previous forecasts that consider only the Delta variant," she said.

Omicron, which the World Health Organization (WHO) labeled a "variant of concern" on Nov. 26, was first discovered in South Africa and prompted countries to introduce travel bans.

However, a preliminary analysis of the initial cases reported to the European Surveillance System (TESSy) suggests that imported or travel-related cases only accounted for 13 percent, while 70 percent were acquired locally.

The EU/EEA countries reporting cases without an epidemiological link to travel are Belgium, Denmark, Finland, Hungary, Norway, the Netherlands, Portugal, Spain, Sweden and Iceland.

Ammon urged countries to act fast to minimize the infection rate.

"Countries should ramp up efforts to increase full vaccination in people not yet vaccinated or only partially vaccinated, as well as to administer booster doses to all eligible as soon as possible," she said.

According to the ECDC, 71.6 percent of the population in the EU/EEA had received at least one vaccine dose by Wednesday, and 67.3 percent were fully vaccinated. However, the uptake was considerably lower in some eastern European countries. In Slovakia and Romania, less than half of the population had received the first dose, and in Bulgaria less than 28 percent of the population had received the first jab.

Sparsely populated Iceland is the only country where more than half of the population have already received the booster dose.

"In the current situation, vaccination alone will not allow us to prevent the impact of the Omicron variant, because there will be no time to address the vaccination gaps that still exist," Ammon warned.

She also urged countries to rapidly reintroduce and strengthen other measures to slow down the spread of the Omicron variant and keep the COVID-19-related burden manageable.

"It remains a priority to use face masks appropriately, telework, prevent crowding in public spaces, reduce crowding on public transport, stay home when ill, maintain hand and respiratory hygiene measures and ensure adequate ventilation in closed spaces. Countries may expect a strong resurgence of cases if they lift these interventions," Ammon said.