Cases of the omicron COVID-19 variant have been spreading rapidly around the world – including in the U.S. – forcing health leaders to take action.
Much remains unknown about the new variant, but nations like the U.S. have acted quickly to respond, implementing controversial travel restrictions and updating mask-wearing guidance.
The concern is that the highly mutated omicron can evade immune response – in addition to its transmissibility.
It is not certain where or when the variant first emerged, although Nigeria's national public health institute said on Dec. 1 it had detected the variant in a sample it collected in October.
Dr. Anthony Fauci, America's top infectious disease expert, said much more will be known about omicron in the next several weeks, and that "we’ll have a much better picture of what the challenge is ahead of us."
But, what is known about omicron and what are symptoms of the variant of concern?
The World Health Organization (WHO) says it could still take some time to get a full understanding of the threat it poses, but the agency says there's no evidence to suggest that symptoms linked to omicron are different from those caused by other variants.
"There is currently no information to suggest that symptoms associated with omicron are different from those from other variants," the agency said.
According to the U.S. Centers for Disease Control and Prevention (CDC), those symptoms include fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, a new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting and diarrhea.
It remains unclear if infection with omicron causes more severe disease and it is set to take weeks to determine whether current coronavirus vaccines are still effective against it.
Vaccine makers have said they are ready to develop new vaccines.
U.S. officials say vaccines will offer at least some degree of protection and urged Americans to get a vaccine and get boosted.
The WHO said Saturday that current vaccines remain effective against severe disease and death. On Monday, it said that the global risk from the variant is "very high" and warned it could lead to surges with "severe consequences."
Cases of the delta variant are still prevalent throughout the world.
The Associated Press contributed to this report.