“The overall global risk associated with the new [variant of concern] Omicron is rated very highly.”
Despite the warnings, some key questions about the variant, first discovered in southern Africa earlier this month, remained unanswered. These include whether it can spread more easily between people, whether it can evade vaccine protection, and whether it causes more serious disease than previous strains.
“A number of researchers in South Africa and other countries are conducting studies to assess these characteristics of Omicron. Depending on these characteristics, if another major wave of Covid-19 occurs, powered by Omicron, the consequences could be severe,” the WHO said.
“Increasing cases, regardless of a change in severity, can place overwhelming demands on health care systems and can lead to increased morbidity and mortality.”
Early evidence from surveillance in South Africa, which reported the variant to the WHO on Nov. 24, suggests the variant has a growth advantage over the highly transmissible Delta strain, which is now dominant.
Infections had risen sharply in the country in recent weeks, coinciding with the detection of the variant, the WHO said on Sunday.
Preliminary evidence also suggested there may be an increased risk of reinfection with Omicron, meaning that the immune systems of people infected with other strains may not be able to recognize the mutated strain.
The variant raised concerns among scientists because of the number of changes concentrated in the spike protein — part of the virus that many vaccines target. The WHO said these included between 26-32 amino acid changes in the spike protein, compared to the reference strain.
Some of these changes have also been seen in other variants such as Delta and Alpha, which are thought to help the virus infect humans or evade the immune system’s antibodies, scientists said.
“Overall, there are significant uncertainties about the magnitude of Omicron’s immune escape potential,” the WHO said in its technical briefing, calling on countries to prepare their health systems for potential spikes.
“Further research is needed to better understand the escape potential against vaccine- and infection-induced immunity. Research efforts are ongoing and data is expected to be available in the coming weeks.”
The WHO also called on countries to strengthen their surveillance systems and ensure that their health systems are prepared.
It asked governments to share as much information as possible about the behavior and characteristics of the virus, the severity of disease in infected people and the effectiveness of disease control measures.
Standard measures such as the use of masks, physical distancing and hand hygiene remained important but may need to be improved with a more communicable variant to prevent the spread, the WHO said.
More than a dozen countries had identified cases of the variant within their borders by Monday afternoon.