The CDC estimated that in the week from Sunday, Nov. 21 through Saturday, Nov. 27 that 99.9 percent of all COVID-19 cases in the United States were from the Delta variant.
The public health agency reported that it uses genomic surveillance to track the proportions of variants circulating.
According to the agency, the Delta variant is more than twice as contagious as previous variants.
Health officials also said some data suggest the variant could cause more severe illness in those who are unvaccinated compared to previous variants.
"The COVID-19 vaccines approved or authorized in the United States are highly effective at preventing severe disease and death, including against the Delta variant," the CDC reported. "But they are not 100% effective, and some fully vaccinated people will become infected (called a breakthrough infection) and experience illness. For all people, the vaccine provides the best protection against serious illness and death."
In the past week, officials have announced emerging cases in the US of the Omicron variant, with eight cases confirmed in New York.
Researchers are working to study the new variant and see how it compares to previous variants.
"At this time, we do not know how quickly Omicron will spread or how severe the symptoms of Omicron will be," said New York Department of Health Commissioner Dr. Mary Bassett. "What we are seeing is that the rise of cases across New York State continues to be traced to the Delta variant. We encourage all New Yorkers to use the best preventative tools we have: get vaccinated, get boosted, and wear a mask."
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