WASHINGTON -- Omicron is spreading rapidly and could become the predominant variant of the coronavirus in the United States "on the order of weeks," Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said Tuesday.
New CDC data showed that omicron now makes up 3% of all sequenced cases of covid-19 across the country, and roughly 13% in New York and New Jersey.
"We've seen it compete pretty aggressively with the delta variant in other countries, namely the U.K. and Denmark, and we are anticipating that we will have more cases" in the U.S., Walensky said in an interview. "It may well be able to outcompete delta."
"What we have seen in these other countries is a doubling time of omicron of around two days, which is really rapid doubling time. So I anticipate if the same were to hold true here that that would be the order of time that we'd start to see it outcompete delta and be the majority," she said.
The worst-case scenario has spooked top health officials, who fear a fresh wave, layered on top of delta and influenza cases in what one described as "a triple whammy," could overwhelm health systems and devastate communities, particularly those with low vaccination rates.
"I'm a lot more alarmed. I'm worried," said Marcus Plescia, chief medical officer for the Association of State and Territorial Health officials. The CDC, normally cautious in its messaging, told public health officials that "we got to get people ready for this," he said.
Plescia noted that the omicron surge, if it materializes as forecast, would be taking place as delta continues its onslaught and during the time of year when influenza cases often peak.
Officials stress that early data shows individuals who are fully vaccinated and received booster shots remain largely protected against severe illness and death from omicron. But they worry about how few Americans have received boosters. More than 54 million people in the United States have gotten the additional shots out of 200 million who are fully vaccinated, according to the CDC.
A second modeling scenario outlines a smaller omicron surge in the spring. It's unclear which scenario is more likely.
The new models have been shared among senior administration officials as they discuss politically fraught decisions about how, when and even whether to take new steps to suppress the virus and keep hospitals from being overwhelmed.
"They're considering the information at the highest levels right now, and thinking through how to get the public to understand what the scenarios mean," said one federal health official familiar with the latest briefing. "It looks daunting."
"The implications of a big wave in January that could swamp hospitals ... we need to take that potential seriously," said the official, who spoke on condition of anonymity without authorization to discuss policy deliberations.
Since the summer, the delta variant has accounted for roughly 99% of all cases in the United States. But omicron has "eclipsed" delta in terms of transmissibility, Walensky said. "I think from a respiratory virus standpoint, this would be high up there among the most transmissible," she said.
While omicron has proven extremely contagious, scientists and public health experts have gotten good news from studies and data on the variant in the weeks since it emerged.
Two doses of the existing vaccines still provide some immunity against the new variant, and a booster dose provides strong protection. Another natural layer of protection, from T cells in the immune system, appears to provide an additional layer of defense against omicron.
Hospitalization rates and average lengths of hospital stays in countries that have seen large surges of omicron cases have been much lower than in previous waves. But Walensky said more data is needed to understand how omicron will affect the U.S. population.
"I think we still need some clarity on, when applied to our United States setting with regards to who's been vaccinated, who's been boosted, who's been previously infected, how severe will omicron be -- and then really how well do our vaccines stack up against the omicron, not only for preventing infection entirely, but in preventing severe disease and hospitalization," Walensky said.
"If you have twice as many infections and half the amount of severe disease, you still have a lot of severe disease," she said. "So we do need to be careful and just make sure people recognize that all of those parameters matter, which is why prevention is so key right now."
The emergence of omicron prompted the largest surge in vaccination rates since the spring, when vaccines first became available. Walensky said roughly 2 million people are getting vaccinated each day -- half with the initial regimen and half with booster shots.
"We know we have many of the tools, and that those tools are effective against all variants -- not just the ones that we've seen, but likely the ones that we haven't seen yet," Walensky said.
She urged Americans to continue to adhere to the measures that have become commonplace over the past two years: wear masks, socially distance and get vaccinated.
While a "massive surge" of omicron cases is possible, Walensky said Americans can still enjoy the holiday season. "Don't rethink your holiday plans," she said. "Just rethink how you're going to do it."
S. AFRICA CASES
In South Africa, omicron is offering more hints about what it may have in store as it spreads around the globe: a highly transmissible virus that may cause less severe disease, and one that can be slowed -- but not stopped -- by today's vaccines.
An analysis Tuesday of data from South Africa, where the variant is driving a surge in infections, suggests the Pfizer vaccine offers less defense against infection from omicron and reduced, but still good, protection from hospitalization.
The findings are preliminary and have not been peer-reviewed -- the gold standard in scientific research -- but they line up with other early data about omicron's behavior, including that it seems to be more easily spread from person to person.
The spread can be seen in Britain, the United States and Denmark, where confirmed omicron cases are increasing at a worrisome pace, said Dr. Jacob Lemieux, who monitors variants for a research collaboration led by Harvard Medical School.
"Omicron is moving extraordinarily fast, faster even than the most pessimistic among us thought it was going to move," Lemieux said.
During past waves of the pandemic, the U.S. could look to Europe and Britain for an early signal of what was coming, Lemieux said. "With omicron, it seems to be happening everywhere all at once with extremely rapid kinetics."
It's unclear whether omicron's rapid spread will overwhelm hospitals. In South Africa, although case numbers are rising, hospital admissions for adults are 29% lower compared with the wave the country experienced in mid-2020, after adjusting for vaccination status, according to the new analysis.
Still, some experts cautioned that it's too soon to draw conclusions since the variant is quite new and hospitalizations can lag weeks behind infections.
When omicron reaches broader populations, more useful information will emerge, said Dr. David Dowdy, an infectious disease epidemiologist at Johns Hopkins Bloomberg School of Public Health.
"To date, omicron has disproportionately infected young adults -- people who probably have more social contacts and are more likely to attend large gatherings," Dowdy said. Young adults may be more likely to be sick without knowing it, have more intense exposures and experience milder disease, he said.
"Our society needs to learn how to wait, rather than either panicking or dismissing early findings," Dowdy said.
U.S. health officials estimate that a small but growing proportion of new infections are due to omicron, and that the rise is particularly dramatic in some places.
Two weeks ago, omicron accounted for less than 0.5% of the coronaviruses that were genetically sequenced in the U.S. That rose to about 3% last week, the CDC reported Tuesday.
But it varies from place to place: It's as high as 13% in the New York/New Jersey area, according to the agency.
The CDC is tracking how quickly the percentage doubles, and as more cases come in, it may be better able to predict whether -- or when -- the omicron variant becomes the dominant version in the U.S, health officials say.
Meanwhile, Pfizer announced Tuesday that its covid-19 pill was found to stave off severe disease in a key clinical trial and that it is likely to work against the omicron variant.
The results underscore the promise of the treatment, which health officials and doctors are counting on, to ease the burden on hospitals as the United States braces for a fourth wave.
If the Food and Drug Administration authorizes the drug, which could happen within days, then patients might begin receiving it by the end of the year. Although supply would be limited at first, public health experts are hopeful that the pills might curb the worst outcomes from the disease, no matter the variant.
Pfizer said its antiviral pill was found to reduce the risk of hospitalization and death by 88% when given to unvaccinated people at high risk of severe covid-19 within five days of the onset of symptoms. The company also said laboratory experiments indicated that the drug will attack a key protein in omicron.
"This is quite amazing and potentially transformative," said Sara Cherry, a virus expert at the Perelman School of Medicine at the University of Pennsylvania who was not involved in the study. "If we could keep people out of hospitals, that would have a huge impact on health care."
Last month, Pfizer asked the FDA to authorize the treatment, known as Paxlovid, for high-risk adults, based on a preliminary batch of data. The new results will undoubtedly strengthen the company's application for the drug, which is meant to be prescribed by a health care provider after a positive virus test and taken at home.
The results, based on an analysis of more than 2,200 unvaccinated volunteers at high risk of severe disease, largely match the company's initial, smaller analysis of the clinical trial, released last month.
Pfizer said that in its final analysis, 0.7% of patients who received Paxlovid were hospitalized within 28 days of entering the trial, and none died. By contrast, 6.5% of patients who received a placebo were hospitalized or had died.
Pfizer also released preliminary data from a separate trial looking at people with a lower risk. These volunteers included vaccinated people who carried a risk factor for severe disease, as well as unvaccinated patients with no risk factors.
Among this group of 662 volunteers, Paxlovid reduced the risk of hospitalization and death by 70%, the company said.
Several public health experts said they thought it was unlikely the FDA would immediately authorize Paxlovid for people at standard risk of becoming severely ill from covid-19 based on the preliminary results, although it may do so eventually.
"Maybe it's something that your physician would think about if you had severe underlying conditions," said Seema Lakdawala, a virus expert at the University of Pittsburgh.
Lakdawala said regulators might consider expanding the drug's use if the benefits outweighed any risks. Paxlovid might shorten the amount of time that people shed the coronavirus, for example, which could reduce how long people have to spend in quarantine. It might even cut down the chances that infected people pass on the virus to others. "All of those would be hugely beneficial," she said.
These possibilities would first have to be confirmed in trials, Lakdawala cautioned. Pfizer is running a trial to see how well Paxlovid can block transmission in households, and expects results in the first half of next year.
Information for this article was contributed by Michael Wilner of the McClatchy Washington Bureau (TNS); by Lena H. Sun, Joel Achenbach, Laurie McGinley and Tyler Pager of The Washington Post; by Andrew Meldrum, Mike Corder, Mike Stobbe and Carla K. Johnson of The Associated Press; and by Carl Zimmer and Rebecca Robbins of The New York Times.