NEW YORK -- This holiday season held promise for Americans, many of whom spent Christmas 2020 in quarantine or away from loved ones due to a nasty winter COVID-19 surge.
Yet in the last week or so, new and worsening problems stemming from the pandemic have damped this excitement. The threat of the new omicron variant looms, businesses and schools close due to COVID-19 exposure and testing lines wrap around city blocks.
Armed with vaccine protection but wary of the unknown, the nation faces a new chapter in the pandemic saga, leaving many to struggle with processing the present and mapping out the future.
Here is what we know about the current state of the pandemic in this country, the science of the omicron variant, the promise of booster shots and the probability of shutdowns designed to slow COVID-19's spread:
The state of COVID in the U.S. and predictions for the surge
The rate of U.S. COVID-19 cases, hospitalizations and deaths has veered upward in the last few weeks, and forecasting models predict that this trend will only accelerate its pace into the winter months.
Two indicators are up about 40% in the last month, according to data from Johns Hopkins University: the seven-day average of new cases topped 120,000, and the total number of hospitalizations stands at more than 68,000.
COVID-19 cases New York City, the global epicenter of the pandemic in its early months, tripled in the last month, officials warned. New Hampshire is now averaging more new daily COVID-19 cases than it did at any other point in the pandemic.
The seven-day average for deaths was 1,286 as of Thursday, an 8% increase from a month ago, data shows.
The Centers for Disease Control and Prevention has been looking at various scenarios involving a triple whammy this winter - COVID-related hospitalizations stemming from omicron or delta, along with cases of seasonal flu. The worst-case scenario is a peak in January with cases slowly trending downward by March, though the data informing the forecast is still sparse.
The agency's latest model predicts as many as 15,600 new virus-related deaths on the week ending Jan. 8, with a total of 845,000 U.S. COVID-19 deaths reported by that date.
This latest surge isn't necessarily stemming from the new omicron variant, despite studies indicating that the mutant strain could be much more contagious than its predecessors.
Hospitals across the country are inundated by patients infected by the delta variant: In Wisconsin, only 4% of ICU beds are available. Michigan's three-month struggle to hamper the virus also continues, with the state reporting more than 500 COVID-19 hospital admissions each day.
"Our delta surge is ongoing and, in fact, accelerating. And on top of that, we're going to add an omicron surge," said Dr. Jacob Lemieux, who monitors variants for a research collaboration led by Harvard Medical School.
MORE: US COVID-19 death toll tops 800,000
Omicron only accounts for about 3% of national COVID-19 cases, though this percentage varies regionally: New variant infections account for 13% of cases in the New York/New Jersey area.
Some experts believe this proportion may be much greater, and many predict that omicron will overtake delta and become the dominant variant in the weeks ahead.
Omicron cases have been doubling nationally every two days and its prevalence increased sevenfold since last week.
How quickly the number of cases doubles, known as "doubling time," can give a preview of what the disease burden could be in a few weeks.
Omicron: What we now know and don't know
Though it's too early to say definitively, the new omicron variant appears to be more contagious than any other variant, including delta, real world data and laboratory tests show.
No reliable estimates show how transmissible the new coronavirus strain is. One U.K. study, though preliminary and small, estimated that omicron is three times more contagious than delta.
Severity and symptoms
Experts still do not know whether infections from omicron cause more severe COVID-19 symptoms nor whether it's deadlier than other coronavirus strains.
Early evidence suggests that the variant may lead to a milder form of the illness: A CDC analysis of 43 omicron-infected people in the U.S. revealed that most did not show severe symptoms. Studies in other countries support this finding.
In the CDC analysis, however, most of the cases examined people who got the COVID-19 vaccine, which dramatically reduces the risk of severe illness.
MORE: How severe is omicron? Expert says variant's 50 mutations could be its downfall
Given the high level of transmission, the variant will undoubtedly generate severe cases, said Bronwyn MacInnis, director of pathogen genomic surveillance at the Broad Institute of MIT and Harvard.
"No matter how severely it affects healthy, fully vaccinated and boosted populations, it will hit the most vulnerable among us the hardest still," she said. "So the elderly, the immunocompromised, other vulnerable populations will still be at greatest risk and still bear the brunt of this."
The variant also seems more likely to cause infections among vaccinated people, but experts assert that the shot still protects against severe forms of the disease.
Laboratory studies show that people who received two doses of the Pfizer or Moderna shots have a lower antibody response to the omicron variant.
Antibodies, however, are only one part of the body's immune system. Studies show that T-cells are less affected by the variant, a possible reason why vaccines prevent severe illness in cases of breakthrough infections.
Another positive finding: Booster shots restore the level of protection provided by the first two doses, according to some of those same studies.
Booster shots and other tools for protection
Getting vaccinated and boosted is the best form of protection against COVID-19 and its omicron variant.
The latest research found that booster shots significantly improved protection against disease.
In one study cited by the CDC, nursing home residents with a booster have 10 times lower rates of getting COVID-19 compared to people who are unvaccinated or vaccinated but without a booster.
A U.K. report also found that two doses of the Pfizer vaccine were 30-40% effective against disease for omicron, but the level of protection increased to 70-80% after a booster shot. Other real-world data echoes these findings.
Dr. Anthony Fauci, the nation's top infectious disease expert, said Wednesday there is no need, for now, for an omicron-specific booster shot. The two-dose mRNA vaccines, the Pfizer and Moderna shots, still appear to offer considerable protection against hospitalization from omicron, Fauci said.
MORE: Fauci says omicron variant can evade vaccine protection, but COVID-19 boosters help
Everyone over the age of 18 is eligible for a booster shot in the United States. Those who received Pfizer or Moderna should wait six months after their original two-dose vaccination, and Johnson & Johnson recipients can get it two months after their first shot.
The CDC allows mixing and matching of booster shots. The shots are the same formulation as the COVID-19 vaccine, but the dosage may be smaller. The booster shot may cause side effects, like pain, redness and swelling, but this response shows that the body is building protection.
Still, only 55 million Americans have received boosters, and 62% of the U.S. population is fully vaccinated.
Health officials said the best bet for slowing the spread is wearing a mask indoors and improving ventilation, in addition to vaccinations and boosters.
They also encourage getting tested before traveling and before holiday gatherings.
"We do have tools in place, and we do know what to do. But we need to make sure that those things happen," said Chrissie Juliano, executive director of Big Cities Health Coalition.
As COVID-19 surges, so does testing
Amid the new surge, the demand for COVID-19 tests is surging ahead of the holiday.
In some places, testing demand is high, rapid tests are hard to find and waits at testing centers are long.
Curative, a company that operates more than 1,600 COVID-19 testing sites in 40 states, reported testing about 55,000 people each day.
"We're continuously seeing increases of about 20 or so percent week over week ... we haven't seen these testing numbers since the peak of the delta surge back in September," said Jamil Sabbagh, who works in operations for Curative.
Home test kits can add a layer of safety by providing on-the-spot results. The tests are not as accurate as the PCR tests done in hospitals and at testing sites. But they have the advantage of giving results within minutes instead of days.
If you're searching for a home test kit, check online and at drugstores. A box with two tests typically costs about $25. If you have health insurance, save your receipt. You may be able to get reimbursed for the cost next year, although it's unclear whether new rules about that will be retroactive.
Residents of some parts of the U.S. can receive free home test kits through a public health effort called Say Yes! COVID Test.
"It's been a phenomenal program," said Matt Schanz, administrator of the Northeast Tri County Health District in northeastern Washington state, where households can get up to eight tests delivered.
"We're social people. We want to gather together and have joyous times during the holiday," Schanz said.
Some health experts are recommending testing twice: Take a test three days before and on the day of a holiday gathering.
"So if you're gathering Christmas Eve, test a few days before and on Christmas Eve as well," said Dr. Kiran Joshi, senior medical officer at the Cook County Department of Public Health in Illinois.
Deja vu? What to know about new wave of cancelations, shutdowns and mandates
The NFL has postponed a handful of games, certain Broadway productions have canceled performances and schools have moved classes online in response to recent COVID-19 outbreaks. New York City's New Year's Eve celebration is still a go, but the city would "watch very carefully" whether to press ahead, New York Mayor Bill de Blasio said.
"At the end of the day, we'll follow the science, and the science will say, 'You need to shut down this performance,'" Broadway League President Charlotte St. Martin told The Associated Press on Thursday.
Businesses ranging from vacation providers to pubs and theaters report a wave of cancellations as customers decide to skip merrymaking for now rather than risk being infected and missing family celebrations later.
Yet as long as people get vaccinated and utilize precautions such as mask-wearing, Fauci said, lockdowns seen last year may not be needed and traveling for a Christmas celebration with other vaccinated people can be done safely.
The White House on Wednesday sought to tamp down any speculation of lockdowns. Jeff Zients, Biden's chief coordinator on the COVID-19 response, said they weren't necessary.
"We know how to keep our kids in school and our businesses open and we're not going to shut down our economy in any way," he told reporters on Wednesday. "We're going to keep our schools and our businesses open."
Still, whether the U.S. faces shutdowns again is largely in the hands of state and local officials who typically have splintered ideas on how to handle surges.
In New York, a statewide mask mandate for all indoor public places would effect Jan. 15 unless businesses already have a vaccine requirement in place. New Orleans is requiring kids ages 5 to 11 be vaccinated before entering public schools, restaurants and other businesses.
And while the U.S. remains reluctant to impose restrictions, other countries are cracking down. On Friday, Denmark decided to close theaters, concert halls, amusement parks and museums in response to a rapid rise in virus cases. In Spain, friends and classmates canceled traditional year-end dinners.
CDC COVID-19 Transmission Levels by U.S. County
Map not displaying correctly? Click here to open in a new window.
The Associated Press, ABC News and CNN Wire contributed to this report.