CDC estimates Omicron variant now makes up 95.4% of all Covid strains circulating in the US as of January 1
The Omicron variant caused an estimated 95 percent of new COVID-19 cases in the U.S. during the week ending January 1, according to the Centers for Disease Control and Prevention (CDC).
In about a month, Omicron has gone from causing under one percent of cases to over 90 percent of cases - outcompeting the previously-dominant Delta variant.
The CDC's variant data come from a modeling system that estimates current variant prevalence from weeks-old sequencing data.
Last week, the CDC revised down its estimate for the share of cases caused by Omicron in mid-December, from 73 percent to 22 percent.
The revision, followed by this week's higher number, shows how the U.S.'s patchy genetic surveillance system is falling behind in tracking this highly contagious variant.
Omicron caused an estimated 95.4% of all new Covid cases in the U.S. last week, according to new CDC data
As Omicron drives record cases across the U.S., testing demand has surged. Pictured: Nurses administer Covid tests in Omicron hotspot Washington, D.C., December 2021
The Omicron variant was first identified in South Africa, Botswana, and Hong Kong in late November.
This variant caught scientists' attention for its high number of mutations and ability to spread more rapidly than any other strain of the coronavirus.
In the weeks since it was identified, Omicron has driven record case numbers in the U.S. and around the world.
Omicron has a 'substantial growth advantage over Delta,' according to the World Health Organization.
The variant was first identified in the U.S. shortly after Thanksgiving, though CDC data now show that it was already spreading during the holiday.
According to new CDC data released Tuesday, Omicron is now causing more than 90 percent of new Covid cases in the U.S.
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In the week ending January 1, the agency estimates that 95.4 percent of new Covid cases across the country were caused by Omicron.
That's about 1.5 times the share of cases caused by Omicron two weeks prior.
The CDC estimates that Omicron caused 38 percent of new Covid cases nationwide in the week ending December 18, and 77 percent of new cases in the week ending December 25.
In the week ending November 27 - which includes Thanksgiving - Omicron was already causing 0.1 percent of new cases nationwide, according to the CDC.
New York and New Jersey continue to have incredibly high Omicron prevalence.
The variant was causing an estimated 98 percent of new cases in this region in the week ending January 1, according to the CDC.
Omicron also caused about 98 percent of new cases in gulf states Texas, Arkansas, Louisiana, New Mexico, and Oklahoma.
New England has the lowest prevalence, according to the latest CDC estimates - still, over 80 percent of new cases in this region were caused by Omicron in the week ending January 1.
New York and New Jersey and the Gulf states region have the highest Omicron prevalence, with the variant causing an estimated 98% of cases last week
CDC variant estimates come from a modeling system called 'Nowcast,' which extrapolates from genetic sequences reported by labs across the country.
It can take two to three weeks from the day a virus specimen is collected from a Covid patient for that virus' sequence to be sent to the CDC.
As a result, the CDC Nowcast system uses data on variant prevalence several weeks ago to estimate the variant prevalence in the present.
More recent estimates can sometimes be inaccurate, and are revised down as the CDC collects and analyzes further sequencing data.
Last week, the CDC revised down its estimate for cases Omicron caused in the week ending December 18 - from 73 percent to just 22 percent.
The agency cited additional data and discrepancies caused by the variant's rapid spread.
In Tuesday's data update, the CDC once again revised estimates for prior weeks.
The agency now estimates that Omicron caused 38 percent of new cases nationwide in the week ending December 18, and 77 percent of new cases in the week ending December 25.
That December 25 estimate was revised up, from 59 percent reported last week.
Uneven Covid testing and sequencing capacity across the country hinders the CDC's ability to track Omicron. Pictured: People wait in line for drive-through Covid testing at a site in Miami, Florida, January 2022
These revisions demonstrate ongoing issues with the CDC's variant surveillance system, including lags of multiple weeks in data collection and uneven reporting.
Cities and other communities served by large, academic research centers tend to have more capacity for genetic sequencing, while rural parts of the country have less access.
As a result, states like New York and California have sequenced thousands of cases in the past month, while states like Louisiana and Oklahoma have only sequenced hundreds.
Still, the CDC's estimates make it clear that Omicron has wholly outcompeted Delta to become the dominant variant in the U.S.
The Delta variant caused less than five percent of new cases in the week ending January 1, according to the CDC's estimates.
Omicron has sparked a new wave of infections, with cases in many states surging above previous records.
On Monday, the U.S. reported over one million new cases - including cases from the holiday weekend's backlog.
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