Speaking at a news briefing, director general Tedros Adhanom Ghebreyesus said more than 90 countries were yet to meet the target of vaccinating 40% of their populations and more than 85% of people in Africa were yet to receive a single dose.
"We mustn't allow this virus a free ride or wave the white flag, especially when so many people around the globe remain unvaccinated," he said.
"This huge spike in infections is being driven by the omicron variant, which is rapidly replacing delta in almost all countries," Tedros said.
He said the majority of people hospitalised around the world with COVID-19 were unvaccinated and that if transmission was not curtailed there was greater risk of another variant emerging that could be even more transmissible, and more deadly, than omicron.