More than half of the population in the World Health Organisation's (WHO) European region could be infected by Omicron within the next two months, the UN agency warned on Tuesday.
Dr Hans Kluge said Omicron "represents a new west to east tidal wave" sweeping through the 53 countries that make up WHO's Europe region.
More than seven million infections were confirmed across the region in the first week of 2022, more than doubling over a two-week period.
"As of 10 January, 26 countries report that over one per cent of their population is catching COVID-19 each week," said Dr Kluge, WHO Europe's regional director.
Fifty countries have now reported Omicron cases with the variant "quickly becoming the dominant virus in western Europe and is now spreading in the Balkans," he added.
"At this rate, the Institute for Health Metrics and Evaluation (IHME) forecasts that more than 50% of the population in the region will be infected in the next six to eight weeks," he said.
Evidence has shown that Omicron is much more transmittable than the original strain of the virus or the Delta variant. It is also more resistant to treatment with fully vaccinated people more likely to get infected or reinfected. Kluge explained that it is because its mutations "enable it to adhere to human cells more easily".
Vaccines remain essential for protection
There were also 20,400 deaths over the past seven days in WHO's Europe region — which also covers parts of central Asia for a total population of about 900 million. This is a slight decline on the previous week when more than 22,600 people lost their lives.
The number of deaths remains below the figures seen during winter 2021 when the Delta variant was spreading fast across Europe.
Kluge stressed that although mortality rates have remained stable, they "continue to be highest in countries with high COVID-19 incidence, combined with lower vaccination uptake".
"Allow me to reiterate that the currently approved vaccines do continue to provide good protection against severe disease and death, including for Omicron," he also emphasised.
There are vast disparities in the vaccination rates within the region.
Denmark, Portugal, and Malta lead the way as more than 80% of their population fully vaccinated. More than half of the population in 28 of the EU/EEA's 31 member states are now fully protected against the risk of severe disease.
But 20 of the region's 53 countries have rates below 50% with Armenia (24%), Bosnia & Herzegovina (22%) and Kyrgyzstan (15.2%) making up the bottom trio.
WHO against measures targeted unvaccinated
The low vaccination rates can be attributed to vaccine inequity and difficulties obtaining doses. The five low-and-low-middle income countries in the region — Ukraine, Uzbekistan, Tajikistan, the Republic of Moldova, and Kyrgyzstan — have all immunised less than a third of their population.
But vaccine hesitancy also accounts for some of the low rates — especially in eastern EU countries.
"Increasing the vaccination uptake is a top priority," Kluge said, arguing however that "we cannot say it is one size for all" and calling for governments to roll out targeted measures to underserved communities.
He also highlighted once more that "countries cannot boost themselves out of any wave alone" and that "it's a do-it-all approach" with measures including wearing face masks and social distancing still very much necessary to combat the spread of the virus.
Dr Catherine Smallwood, WHO Europe's Senior Emergency Officer, meanwhile said: "We do not recommend distinguishing between vaccinated and unvaccinated groups because that will go further in terms of exacerbating inequities in the population".
A number of European countries, including Germany, Austria and Italy, have now limited the number of public places unvaccinated people can access such as bars, restaurants and public transport. France is expected to follow suit later this month, with President Emmanuel Macron sparking controversy when he said "the unvaccinated, I want to really annoy them until the bitter end".
Best 'hold our guns' on Omicron severity
Kluge's address comes just a few days after the WHO chief, Dr Tedros Ghebreyesus Adhanom, warned against describing Omicron as "mild", stressing that "just like previous variants, Omicron is hospitalising people and it is killing people".
Dr Smallwood added on Tuesday that although there is a slight decrease in infection severity between Omicron and Delta, that cannot fully explain the significant number of milder infections.
"The reason we're seeing a lot more milder infections across Western Europe, in Israel, is because of the high vaccination uptake in our population. That immunity is basically meaning that we're able to tolerate from a public health perspective a higher degree of infection in the population," she said.
"We cannot generalise that scenario in all contexts and in countries where vaccination rates are much lower than the very high rates that are at present in Western Europe, including in booster vaccination.
"We're yet to see how Omicron will pan out in a situation where they are more people susceptible or naive, immunologically naive, to SARS-COV-2. And that's where we need to hold our guns, be very cautious and not jump to any conclusions about changing the strategy and letting COVID spread," she warned.