Originally Published: 30 DEC 21 10:54 ET

Updated: 30 DEC 21 11:07 ET

By Madeline Holcombe, CNN

(CNN) -- A new year is coming, and it brings along concerns over imminent holiday celebrations in light of the Omicron variant.

The coronavirus strain, the latest "variant of concern," according to the World Health Organization, is spreading across the United States quickly. In the next week or 10 days, the virus circulating from holiday gatherings could boost daily numbers to more than half a million, estimates CNN Medical Analyst Dr. Jonathan Reiner, a professor of medicine at George Washington University.

People often ring in the new year with large, raucous parties, so health experts are cautioning the public to keep the virus in mind. Some cities across the world are canceling or scaling back events to protect against spread.

"There is so much coronavirus in communities around the country that you should assume that Omicron is likely to be at whatever gathering you're going to, and with that in mind, your decision-making should take that into account," said CNN Medical Analyst Dr. Leana Wen, who is an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health.

Not all gatherings pose the same risk. How many people are together, where the party is located and who is in attendance all make a big impact on how safe New Year's celebrations may be.

"This is a very high-risk time when it comes to coronavirus," Wen said. "That doesn't mean that everyone should stay home and not do anything, but rather that they need to weigh their own medical circumstances and their risk tolerance."

The size of the gatherings

When it comes to getting together in groups in the time of Covid-19, "the risk is never zero," said Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases.

The risk can be lowered, however.

"We feel you should continue to go through with those plans of having a home-related, vaccinated, boosted gathering with family and close friends who are also vaccinated and boosted," added Fauci, top medical adviser to President Joe Biden, during the White House's Covid-19 response team briefing Wednesday.

Those small gatherings with vaccinated people are low-risk events, Wen said, and they can be made even safer by reducing exposure with masks and distancing leading up to the event. Then afterward, it's important to be mindful of exposing people who are at high risk for serious infection, such as those who are older or have weakened immune systems.

"If someone makes that decision, they should make sure that prior to seeing vulnerable relatives or friends, for example, visiting an elderly aunt in a nursing home or getting together with unvaccinated young children that you should wait at least three days and then you get a negative test prior to seeing that person," Wen said.

As parties grow in number, they also grow in risk of infection, the health experts said.

"If your plans are to go to a 40-to-50-person New Year's Eve party with all the bells and whistles and everybody hugging and kissing and wishing each other a Happy New Year? I would strongly recommend that, this year, we do not do that," Fauci said.

Wen added that the size is a problem for multiple reasons.

"The larger the group, the higher the risk because you are assuming the risk of each person there and the larger the group, the less likely you are to fully understand people's vaccination status and their exposure," Wen said.

What you are doing before and after

Some large gatherings, albeit scaled down, like the one held in New York City's Times Square, are still moving forward. An outdoor setting lowers the risk of infectious spread, especially with masks, according to Fauci, but big crowds raise it again — and events around the party can raise it even more.

"My concern is that they are going to go to a restaurant beforehand, a bar after getting together with friends," Wen said. "So, people should keep in mind that risk is cumulative."

People are going to take risks, especially over occasions traditionally marked by gathering, but the key is to be discerning about how those risks of exposure are taken.

Even if you are working remotely, vaccinated and making choices to reduce your risk profile, you have to trust that others around you in indoor settings are making similar choices to keep your chances of infection at a gathering low, Emory University Hospital Associate Chief Medical Officer Dr. Colleen Kraft told CNN's Poppy Harlow on Monday.

Many people aren't making those choices, however, Kraft added.

"The more high-risk events that people go to, the more risk adds one on top of another," Wen said. "You should choose the event of the highest value to you but reduce your exposure to other high-risk events."