Live updates: follow the latest news on Covid-19 variant Omicron
The Omicron variant is likely to spread internationally, posing a "very high" global risk where Covid-19 surges could have "severe consequences" in some areas, the World Health Organisation (WHO) said on Monday.
The UN health agency issued technical advice urging its 194 member states to accelerate vaccination of high-priority groups and "ensure mitigation plans are in place" to maintain essential health services.
"Omicron has an unprecedented number of spike mutations, some of which are concerning for their potential impact on the trajectory of the pandemic," it said.
"The overall global risk related to the new variant of concern Omicron is assessed as very high."
Speaking at the World Health Assembly on Monday, WHO head Dr Tedros Adhanom Ghebreyesus warned that the emergence of more dangerous variants was a consequence of poor coordination in the global virus response.
"Omicron’s very emergence is another reminder that although many of us might think we are done with Covid-19, it is not done with us. We are living through a cycle of panic and neglect. Hard-won gains could vanish in an instant," he said.
"Omicron demonstrates just why the world needs a new accord on pandemics: our current system disincentivises countries from alerting others to threats that will inevitably land on their shores," he added.
An accord on coordinating a global response to the current and future pandemics is one of the key issues being discussed by participants at the World Health Assembly.
To date, no deaths linked to Omicron had been reported, though further research was needed to assess Omicron's potential to escape protection against immunity induced by vaccines and previous infections, the WHO said.
"Increasing cases, regardless of a change in severity, may pose overwhelming demands on health care systems and may lead to increased morbidity and mortality. The impact on vulnerable populations would be substantial, particularly in countries with low vaccination coverage," it said.
The variant was first reported to WHO on November 24 from South Africa, where infections have risen steeply.
It has since spread around the world, with new cases found in the Netherlands, Denmark and Australia even as more countries imposed travel restrictions to try to seal themselves off. Japan said on Monday it would close its borders to foreigners, joining Israel in taking the toughest measures.
The WHO, in its latest guidance, urged that countries to use a "risk-based approach to adjust international travel measures in a timely manner". Further advice would be forthcoming, it said.
"The presence of multiple mutations of the spike protein in the receptor-binding domain suggests that Omicron may have a high likelihood of immune escape from antibody-mediated protection. However, immune escape potential from cell-mediated immunity is more difficult to predict," it said.
"Overall, there are considerable uncertainties in the magnitude of immune escape potential of Omicron."
More data was expected in coming weeks.
"Covid-19 cases and infections are expected in vaccinated persons, albeit in a small and predictable proportion," the UN agency said.
A top South African infectious disease expert said Omicron appears to be more transmissible than previous variants, including to people with immunity from vaccination or prior infection. South African cases are likely to top 10,000 a day this week, rocketing up from 2,858 on Sunday and barely 300 a day two weeks ago, Professor Salim Abdool Karim said.
But he added that it was too early to say whether symptoms were more severe and said existing Covid-19 vaccines are probably effective at stopping Omicron from causing severe illness.