Omicron accounted for 73 percent of new infections last week, federal health officials announced Monday, Dec. 20.
That's nearly a six-fold increase in only one week, the Centers for Disease Control and Prevention (CDC) said.
The first Omicron-related death in the United States was confirmed in Harris County, Texas - a man in his 50s. It has not been reported whether he was vaccinated or had any pre-existing conditions.
In some parts of the country, nearly 90 percent of new cases are Omicron, the CDC said, adding that the number of Omicron-linked cases has been doubling every two to three days.
In just two weeks, 26 states have seen cases rise 10 percent or more, including New York and Massachusetts, and in seven states, including Connecticut and New Jersey, Omicron cases have risen 50 percent.
In New York, cases have tripled in just a week, with the state setting new daily records for cases for four straight days.
The first US Omicron case was identified on Wednesday, Dec. 1.
The San Francisco Department of Health said the individual was a traveler who returned from South Africa on Monday, Nov. 22, and tested positive for COVID on Monday, Nov. 29. The individual was fully vaccinated and experienced mild symptoms.
Though the surge in cases is coming during one of the busiest travel times of the year, prior to Christmas and the New Year, officials say vaccinations and booster shots and wearing masks indoors in public settings appear effective in preventing severe cases.
“We’ve seen cases of Omicron among those who are both vaccinated and boosted and we believe these cases are milder or asymptomatic because of vaccine protection,” said Centers for Disease Control and Prevention (CDC) Director Dr. Rochelle Walensky said during a White House COVID-19 briefing on Friday, Dec. 17.
Preliminary lab studies indicate Omicron may not attack the lungs like other variants.
Omicron "replicates, multiples very well in the upper airway (above the neck), but less well in the lung," Top Infectious Disease Specialist Dr. William Schaffner of Vanderbilt University Medical Center told NBC News.
"It's not March 2020 or even December 2020 -- just to keep things in perspective," New York Gov. Kathy Hochul said.
For info on a study listing the Top 5 symptoms for the Omicron strain, click here.
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