On 7 January, many Orthodox Copts and other Orthodox Christians (including those in Russia and Ethiopia) celebrate their Christmas Day.
The difference in date lies simply in the calendar being used.
Many Orthodox Christians follow the Julian calendar, which predates the Gregorian one introduced by Pope Gregory in 1582.
The calendars are 13 days apart, pushing celebrations for much of the Arab region's Christians into the second week of January.
Coptic Christians form the largest Christian community in the Middle East, most of them in Egypt where roughly 10 percent of the 95 million population are Copts, although estimates vary.
At the Martyrs Church in Khartoum, Sudanese Copts attended the Christmas midnight mass.
"Most of the people did not come" says Niveen Amin.
"This is because they are afraid, so the church was almost empty. They are still afraid, even if there is no disease. I hope that next year it will disappear, and for all of Sudan to be happy and to celebrate with us. This year is a different celebration, because most of the churches are closed. I hope next year all the churches will be open and celebrating Christmas. " the Sudanese Copt explained.
The Orthodox Christian faith uses the old Julian calendar in which Christmas falls after the date in the more widespread Gregorian calendar.
On Wednesday afternoon -- Christmas Eve for Ethiopian Orthodox Christians -- prices of basic goods soared in the dusty marketplace near the Umm Raquuba refugee camp in Sudan as people scrambled to buy food to celebrate.
"Everything is very expensive here," said Haftoun Gebremikail, shopping at the market for something to mark the holiday.
"I just want to buy some lamb, sugar and milk -- or anything! It's Christmas."
But many struggle to find anything within their budget.
Demand is high. The sprawling camp is already close to capacity, while the United Nations this week opened a new camp to cope with arrivals.
Refugees are continuing to flee the unrest in Ethiopia's Tigray region, with 800 people having crossed the border into Sudan since the New Year, according to the UN.
Many of the refugees fled with only the clothes they were wearing, forced from their homes as fighting raged nearby.