The virus that causes COVID-19 is constantly changing and adapting. New variants of the virus are expected to occur, as has been the case in the United States and globally throughout the pandemic. A Variant of Concern (VOC) is "a variant for which there is evidence of an increase in transmissibility, more severe disease (for example, increased hospitalizations or deaths), significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures."
Currently, there are two VOCs in the United States: Delta and Omicron. The Delta variant is more than 2 times as contagious and causes more infections and more severe infection than earlier forms of the virus. The Omicron variant was first classified as a VOC in the United States on November 30, 2021. In the wake of its emergence, local, state, and federal health officials are closely monitoring its movement and characteristics. More research is needed to know how Omicron affects the risk of severe infection or death and how the vaccines fare against it. Still, all approved COVID-19 vaccines reduce the risk of severe illness, hospitalization, and death from COVID-19.
Omicron has been confirmed in Colorado, including in Weld County. Omicron became the main variant circulating in Colorado starting the week of December 19, 2021, and has been the dominant variant in the United States, including in the Mountain West region.
For more information about Delta, Omicron, and other variants, go to the CDC's "Variants of the Virus" webpage.