Omicron Cases in the U.S. Likely to Rise, Officials Say

Several dozen cases of the new Omicron variant of the coronavirus have been identified in the United States, a number that is “likely to rise,” Dr. Rochelle P. Walensky, the director of the Centers for Disease Control and Prevention, said on Sunday on ABC’s “This Week.”

At least 17 states have detected cases, including in some people who have no known history of recent travel abroad, which experts have said suggests community spread of the variant in the United States.

Genetic sequencing is required to determine which variant an infected patient has. In recent months the United States has greatly expanded sequencing efforts, but the process takes time. The C.D.C., for instance, typically takes about 10 days to yield results. According to Dr. Walensky, about 14 percent of all positive P.C.R. tests in the United States are being sequenced.

“What we don’t yet know is how transmissible it will be, how well our vaccines will work, whether it will lead to more severe disease,” Dr. Walensky said.

American officials are in frequent communication with experts in South Africa where the variant is now widespread, Dr. Anthony S. Fauci, the nation’s leading infectious disease doctor, said Sunday on CNN’s “State of the Union.”

How quickly Omicron will spread in the United States, where the highly contagious Delta variant now accounts for 99.9 percent of all cases, remains unknown, Dr. Fauci said. “What’s going to happen when you have those two competing with each other?” he said, adding that, “we have really got to be careful” in assessing how severe Omicron might end up being.

A new report from South Africa has fueled hopes that the variant may not cause serious disease, though it remains far too early to conclude that, experts say. The report focuses primarily on 42 patients in a hospital in Gauteng province, the center of the nation’s Omicron outbreak.

Although the researchers were not able to confirm that all the cases were caused by Omicron, the majority of patients with the virus did not require supplemental oxygen, the report says, and many were not hospitalized for Covid-19 itself. Instead they tested positive for the virus after being admitted for other reasons.

“This is a picture that has not been seen in previous waves,” wrote Dr. Fareed Abdullah, who directs the Office of AIDS and TB Research at the South African Medical Research Council and is the author of the new report.

But the findings come with major caveats, including the fact the patients were younger than during previous waves, and thus less likely to have severe disease. The data also accounts for just the first two weeks of the outbreak — hospitalizations and deaths are often a lagging indicator and could rise in the coming weeks.

Omicron’s rapid spread still poses risks, Dr. Maria Van Kerkhove, the World Health Organization’s technical lead for coronavirus response, said on Sunday on CBS’s “Face the Nation.”

“Even if we have a large number of cases that are mild, some of those individuals will need hospitalizations, they will need to go into I.C.U., and some people will die,” she said. “And so more cases can mean more hospitalizations, and more hospitalizations could mean more deaths.”

She also urged governments to take swift action by increasing vaccination and encouraging mask wearing, distancing and ventilation to tamp down the spread of Omicron and Delta.

The Biden administration recently announced plans to expand its booster campaign and increase access to rapid tests. On Monday, the United States will begin requiring all incoming air travelers to show proof of a negative test taken the day before departure, regardless of their vaccination status or citizenship.

On Sunday, officials also defended the government’s ban on travelers from eight countries in southern Africa. The ban has been criticized for being both unhelpful and overly punitive.

“That ban was done at a time when we were really in the dark,” Dr. Fauci said, noting that it was intended to buy officials time to gather more information about Omicron. But now that more information is coming in from around the world, officials are frequently re-evaluating the ban, he said.

“Hopefully, we will be able to lift that ban within a quite reasonable period of time,” he said, adding that “we all feel very badly about the hardship” that it put on southern Africa.

But officials dismissed the possibility of domestic travel restrictions, noting that they would be impractical. “That would be extremely onerous for people who are trying to get around the country for things like holidays,” Dr. Francis S. Collins, the National Institutes of Health director, said on NBC’s “Meet the Press” on Sunday. “And I don’t know how much we’d gain by it.”