650K Omicron COVID Infections Occurred in U.S. Last Week, CDC Data Shows

The rate of Omicron COVID-19 infections in the U.S. skyrocketed last week, with the variant responsible for a majority of new infections, the Centers for Disease Control and Prevention (CDC) said on Monday.

The CDC said there were more than 650,000 Omicron infections last week in the U.S., nearly six times the number of reported cases from one week earlier, and that 73 percent of the new infections were from the newest variant.

In some regions like New York, the Pacific Northwest, the Southeast and the industrial Midwest, Omicron is responsible for about 90 percent or more of new cases.

Dr. Amerh Adalja, a senior scholar at Johns Hopkins Center for Health and Security, said he's not surprised the U.S. is seeing an increase in Omicron cases given what happened in countries like South African and the U.K. The CDC's numbers showing Omicron had overtaken Delta for new infections was to be expected.

"All of us have a date with Omicron," Adalja said. "If you're going to interact with society, if you're going to have any type of life, Omicron will be something you encounter, and the best way you can encounter this is to be fully vaccinated."

It's too soon to tell if Omicron is milder compared to previous variants, said Dr. Eric Topol, head of the Scripps Research Translational Institute.

The CDC does not have an estimate on how many hospitalizations or deaths have resulted from Omicron, officials said.

Los Angeles International Airport, COVID-19
The rate of Omicron COVID-19 infections in the U.S. skyrocketed last week, with the variant responsible for a majority of new infections, the Centers for Disease Control and Prevention said. Above, travelers wait for a shuttle but to arrive at the Los Angeles International Airport on December 20, 2021. The Los Angeles County Department of Public Health reported more than 3,500 new cases of COVID-19 on Sunday as the number of daily new cases tripled over the past week. Jae C. Hong/AP Photo

CDC Director Dr. Rochelle Walensky said the new numbers reflect the kind of growth seen in other countries.

"These numbers are stark, but they're not surprising," she said.

Scientists in Africa first sounded the alarm about Omicron less than a month ago and on November 26 the World Health Organization designated it as a "variant of concern." The mutant has since shown up in about 90 countries.

Much about the Omicron variant remains unknown, including whether it causes more or less severe illness. Early studies suggest the vaccinated will need a booster shot for the best chance at preventing Omicron infection but even without the extra dose, vaccination still should offer strong protection against severe illness and death.

Adalja predicted a spread over the holidays, including breakthrough infections among the vaccinated and serious complications among the unvaccinated that could stress hospitals already burdened by Delta.

Topol said other countries had seen Omicron's fast growth, but the U.S. data showed "a remarkable jump in such a short time."

CDC's estimates are based on thousands of coronavirus specimens collected each week through university and commercial laboratories and state and local health departments. Scientists analyze their genetic sequences to determine which versions of the COVID-19 viruses are most abundant.

On Monday, the CDC revised its estimate for omicron cases for the week that ended December 11, after analyzing more samples. About 13 percent of the cases that week were from Omicron, not the 3 percent previously reported. The week before, Omicron accounted for just 0.4 percent of cases.

Though there remain a lot of new infections caused by the Delta variant, "I anticipate that over time that Delta will be crowded out by Omicron," Walensky said.

The Associated Press contributed to this report.

COVID-19 Testing New York City
Long lines form at a COVID-19 testing site in front of Trinity Church on Wall Street during the week before Christmas as the Omicron variant causes an increase in cases and fears of holiday event cancellations, on December 20, 2021, in New York City. Roy Rochlin/Getty Images