The World Health Organization is urging people to reconsider holiday gatherings and travel plans for safety's sake, as the Omicron variant spreads rapidly across more countries.

Dr Tedros Adhanom Ghebreyesus, Director-General of the WHO, warned in a Monday briefing that there is now "consistent evidence that Omicron is spreading significantly faster than the Delta variant," and that holiday festivities would in many places lead to "increased cases, overwhelmed health systems and more deaths".

He urged both leaders and individuals to make the right decisions around cancelling or postponing holiday events.

"An event cancelled is better than a life cancelled," he said.

The WHO had warned last month, when Omicron was first brought to its attention, that the variant presents a very high global risk due to its high transmissibility and its ability to infect even vaccinated individuals and those who have previously contracted COVID-19. Already, the variant has been found in 89 countries and community transmission is so rapid that the number of cases can double within three days, according to a WHO update from last Saturday. In the US, the Center for Disease Control and Prevention has already reported that Omicron is now the dominant strain in the country.

In the Monday briefing, WHO Chief Scientist Dr Soumya Swaminathan warned that Omicron may not in fact be the mild variant it was originally taken for, pointing out that the initial data from South Africa may have been skewed by high levels of immunity among the population.

"With the numbers going up all health systems are going to be under strain," she warned,