Early Data on Omicron
As many Americans and others around the globe prepare for holiday travel and get-togethers, the omicron variant continues to be a concern. While the available data on transmission, vaccine effectiveness and severity of disease are still preliminary, here’s what we’ve learned so far.
Transmission
Omicron has quickly taken over as the dominant variant in the United States. On Dec. 1, the country had its first confirmed case, and by the week ending Dec. 25, omicron accounted for an estimated 59% of new cases, according to the Centers for Disease Control and Prevention. (See “Variant Proportions.”)
Overall, the seven-day average of new cases in the U.S., due to any variant, has gone up, numbering about 80,000 on Nov. 29 and 135,000 on Dec. 19.
The World Health Organization on Dec. 17 that omicron has been identified in 89 countries and that there is “consistent evidence” the variant “has a substantial growth advantage” over delta. “It is spreading significantly faster than the Delta variant in countries with documented community transmission, with a doubling time between 1.5–3 days,” the WHO said in a technical brief. “Omicron is spreading rapidly in countries with high levels of population immunity and it remains uncertain to what extent the observed rapid growth rate can be attributed to immune evasion,
