London CNN  — 

South Africa, the United Kingdom and Denmark are three of the countries where the Omicron variant is now surging, less than a month after it was first detected.

The UK is seeking to vaccinate itself out of the crisis, with an accelerated campaign to give a third Covid-19 vaccine dose to all eligible adults by the end of December.

In South Africa, meanwhile, researchers say early data suggests Omicron causes milder symptoms – but it’s still unclear how much of a role immunity from vaccination or previous infection plays.

Denmark is mulling new restrictions in an attempt to control a spike of new cases.

So what can other countries learn from their experience?

It’s too late to keep Omicron out

Despite many nations imposing a slew of travel restrictions, the variant has spread quickly around the globe.

World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus told a news briefing Tuesday that 77 countries have now reported cases of Omicron, and “the reality is that Omicron is probably in most countries, even if it hasn’t been detected yet.”

“Omicron is spreading at a rate we have not seen with any previous variant,” Tedros said. “We’re concerned that people are dismissing Omicron as mild. Surely, we have learned by now that we underestimate this virus at our peril.”