The Omicron variant of the coronavirus is spreading faster than the Delta variant and is causing infections in people already vaccinated or who have recovered from the Covid-19 disease, the head of the World Health Organization (WHO) said on Monday.

WHO chief scientist Soumya Swaminathan added it would be "unwise" to conclude from early evidence that Omicron was a milder variant than previous ones.

"... with the numbers going up, all health systems are going to be under strain," Soumya told Geneva-based journalists...