Christmas is coming. Around the world, people who celebrate the end of the year holidays are taking time off and heading home to see friends and relatives. They include aid workers fighting Ebola in Sierra Leone, Liberia and Guinea.

And they include residents of the three countries hardest hit by the Ebola epidemic.

It worries Dr. Dan Kelly. And officials in Sierra Leone were concerned enough to limit public gatherings for the holidays.

“The way Sierra Leoneans celebrate the holiday is traveling back to their home villages,” said Kelly, a founder of the nonprofit Wellbody Alliance who’s been working in Sierra Leone since the epidemic began.

Right now, Ebola is raging out of control in Sierra Leone’s capital of Freetown. It’s barely under control in outlying districts like Kono and Kenema. The epidemic started as people traveled across the region’s porous borders, and this will be the first Christmas and New Year holiday since the epidemic started.

“You have a couple of million people in Freetown and I’d say 50-plus percent of those people in Freetown are interested in traveling back to remote villages for the holidays,” Kelly told NBC News.

“And they’ll spend a week there,” added Kelly, who’s worked in Sierra Leone on and off since 2006. “It could spread Ebola all around the country and just create hundreds of hotspots for sure.”

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Sierra Leone’s president, Ernest Bai Koroma, says travel between all parts of the country has been restricted as part of "Operation Western Area Surge," an effort to get a handle on the epidemic. He says public gatherings will be strictly controlled in the run-up to Christmas.

"All it takes to set off a new series of cases is one person who is infected with the Ebola virus but not yet sick travelling to another place, falling ill there, and passing the virus on to others."

Kelly is skeptical about how well that might work. “They can’t control it completely,” he said.

And the holiday spirit might work in other ways to disrupt efforts to control the virus. “I think there will be tension between international community trying to go, go, go and the local Sierra Leoneans just trying to spend time with their families and just do what they do every Christmas. It’s natural,” Kelly said.

“There is going to be less surveillance activity. Things are going to slow down in a way that may let Ebola speed up.”

Dr. Darin Portnoy, vice president of the international board of Medecins Sans Frontieres (MSF or Doctors Without Borders), agrees it’s a worry.

“I think there is every reason to be concerned about what will happen with people getting together and moving around over the holidays,” Portnoy told NBC News.

“The whole reason that the disease has been able to move around, in part, is because of common borders, roads that connect countries, relationships between families — especially in areas where these borders come together,” added Portnoy, who is also an attending physician at Montefiore Hospital in New York.

The current epidemic of Ebola started as an outbreak in Guinea, and was carried to Sierra Leone and later to Liberia by people whose relationships predate the current borders. Ebola had never been seen in West Africa before but viral hemorrhagic fevers are not uncommon at all — there’s Lassa, and dengue, and malaria causes similar symptoms, also — so people had no idea that this one was different.

Ebola has infected close to 19,000 people and killed 7,000 of them. Officials hope to have it under control by the middle of next year, but say it’ll take a concerted effort to do so.

Sierra Leone is mostly Muslim, but at least a quarter of the population is Christian and the Christmas-New Year holiday is popular. Liberia's majority Christian, and while Guinea is mostly Muslim, the former French colony celebrates Christmas as a national holiday.

“All it takes to set off a new series of cases is one person who is infected with the Ebola virus but not yet sick travelling to another place, falling ill there, and passing the virus on to others,” said Kathryn Jacobsen, a professor of global health epidemiology at George Mason University.

It happened just last month in Sierra Leone’s eastern province of Kono, which had only seen the occasional Ebola case. Then it flared up at the end of November, overwhelming hospital workers. “We had a surge. We had an Ebola surge,” said Kelly, who called in help from the CDC, World Health Organization and British military to help get it under control.

But Dr. Peter Kilmarx, country director for the Centers for Disease Control and Prevention in Zimbabwe, is less concerned. “I know they’ve been talking about banning holiday gatherings,” he said. But, he added, the epidemic may have gone past the point where travel would affect it.

“There’s cases everywhere anyway,” he said.