While data from the Centers for Disease Control and Prevention shows that the Delta variant has accounted for nearly every COVID-19 in the US since the summer, there are concerns that the recently discovered Omicron variant will increase infections and make the pandemic longer.
The Delta variant, discovered in late 2020, had little presence in the US until May 2021. Until mid-June, the older Alpha variant was the dominant strain of COVID-19.
As of late December, Omicron represents 73% of US cases.
Health officials are researching how Omicron differs from other variants. While the CDC expects Omicron to spread more quickly than Delta, it is unclear how easily it may spread. The health agency does not have any information on the severity of Omicron infections or the effectiveness of existing treatments against the strain. The agency expects vaccination to prevent severe illness.
Omicron and Delta are the only variants considered Variants of Concern (VOC) as of December. The designation applies to variants that show attributes, including an increase in transmissibility, more severe disease, or a reduction in antibody effectiveness.
Delta has increased transmissibility compared to earlier strains. Existing antibody treatments are effective against the most prevalent version of Delta (B.1.617.2), though less so against strarer forms (AY.1 and AY.2).
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