Just 54 percent of people in the European region are vaccinated against the coronavirus, according to an official with the Europe branch of the World Health Organization (WHO).
"There are [around] 45 percent who are unvaccinated or not fully vaccinated, that's a bigger issue for our policy and decision-makers right now - driving up vaccination rates," he added.
The WHO's Europe branch includes 53 countries in Europe and Central Asia.
The rate of full vaccination in the European Union itself is slightly higher, at 65 percent.
As countries in Europe grapple with the region's latest wave of coronavirus cases, Butler said the WHO had no position on countries implementing vaccine mandates to combat the virus. However, he added that mandates were a "very delicate" issue.
"It polarizes, you risk marginalizing [people] and it can come at the expense of trust and social inclusion. So it's a very delicate measure, a last-resort measure. Lessons of history have shown us that where vaccines are mandated or made compulsory, there is an erosion of trust and we have seen this polarization," he said.
WHO Europe said in a statement Tuesday that the region could see 700,000 more deaths in the upcoming months due to the spike in cases.
Following that statement, the EU said Wednesday that booster shots should be considered for all adults, reversing its prior policy.