Early studies showed that there was a reduced risk of hospitalization for omicron compared to delta, there also appears to be a reduced risk of severity in both younger and older people, according to the WHO.

According to the WHO's head in clinical management, Janet Diaz, the impact on the elderly is one of the big unanswered questions about the new variant, since most of the cases studied to date have been in younger people.

"Although omicron appears to be less severe compared to delta, especially in vaccinees, that does not mean it should be classified as mild," said Director General Tedros Ghebreyesus at the same briefing in Geneva.

On the other hand, the official reinforced the recurrent calls for greater efficiency in vaccine distribution. Based on the current rate, 109 countries will not meet the WHO target of immunizing 70% of the world's population by July.

"Reinforcement after reinforcement in a small number of countries will not end a pandemic as long as thousands of people remain completely unprotected," he said.

The WHO said cases increased 71%, or 9.5 million, in the week to January 2 from the previous week, while deaths fell 10%, or 41,000.

Another variant, B.1.640, - first documented in several countries in September 2021 - is among those being monitored, although it is not yet circulating widely, the WHO said.