The Omicron variant of COVID-19 is spreading at an unprecedented rate across the globe, the head of the World Health Organization has warned.

Iran PressEurope: WHO Director-General Tedros Adhanom Ghebreyesus said Tuesday that the new variant has already been confirmed in 77 nations, though it is spreading “probably in most countries.”

“Omicron is spreading at a rate we have not seen with any previous variant,” Tedros said at a press briefing in Geneva.

Tedros said he was concerned that people have been “dismissing Omicron as mild.

“Surely we have learned by now that we underestimate this virus at our peril. Even if Omicron does cause less severe disease, the sheer number of cases could once again overwhelm unprepared health systems,” Tedros said.

Tedros warned that “vaccines alone” won’t be enough to tackle the latest variant.

“It’s not vaccines instead of masks. It’s not vaccines instead of distancing. It’s not vaccines instead ventilation or hand hygiene. Do it all. Do it consistently. Do it well,” Tedros said.

Experts have raised concerns that Omicron, which was first detected last month in South Africa, maybe more resistant to existing vaccines than earlier variants.

Preliminary studies, however, have indicated that a booster shot enhances protection against the variant.