The Omicron variant of COVID-19 is dangerous and especially so for those who have not been vaccinated against the disease, the World Health Organization (WHO) said Wednesday.

"While Omicron causes less severe disease than Delta, it remains a dangerous virus, particularly for those who are unvaccinated," WHO chief Tedros Adhanom Ghebreyesus told a press conference.

"In Africa, over 85 percent of people are yet to receive a single dose of vaccine. We can't end the acute phase of the pandemic unless we close this gap," Tedros said.