On 26 November 2021, WHO designated the variant B.1.1.529 a variant of concern (VOC), named Omicron, on the advice of WHO’s Technical Advisory Group of Virus Evolution (TAG-VE). This decision was based on the evidence presented to the TAG-VE that Omicron has several mutations that may have an impact on how it behaved, for example, on how easily it spreads or the severity of the illness it causes. A summary of what is currently known about SARS-CoV-2 B.1.1.529 (variant of concern Omicron), can be found here.
On 3 December 2021, the Mexico Ministry of Health reported the first detected case of Omicron Variant of Concern. The full report is available here.