KHARTOUM, Sudan — Standing at the junction of two of downtown’s busiest avenues, Ahmed, a slim young man with yellowing teeth and torn drawstring trousers, cuts a shifty figure as he slowly paces around a shopping arcade, steps from the presidential palace.

Nervously eyeing nearby traffic policemen, he periodically wipes the sweat from his brow in the almost 50 C (122 F) heat, checks his reflection in an airline office window, and quickly sidles up to passersby who he feels might take an interest in his wares.

“Would you like to change dollars? I give good rates,” he says in a voice that’s little more than a whisper. “How about some cigarettes? Or perhaps you’d like a vaccination card?”

Black market currency dealers are a longtime fixture in Sudan, where two decades of trade sanctions have battered the economy, cut off access to Western banks, and empowered those with American bills, who can buy 30 percent more Sudanese pounds on the street than they can when exchanging at the official rate. The trade in fake Yellow Fever certificates is, however, a more recent development, which has sparked concern among international health organizations that see proof of inoculation before travel as a prime means of stymieing the disease’s spread.

But such worries count for little among those who are struggling to stay afloat amid high inflation and limited job prospects. With vaccinations usually costing about 150 Sudanese pounds (about $25) from government clinics, some families—particularly those with many children—are keen to save cash by paying out a more manageable 50 pounds ($8) to roadside card vendors. Others maintain that the procedure is a pointless requirement foisted upon Sudan by foreign countries, and they’re subsequently intent on sparing themselves a run-in with a needle.

“It’s difficult to get accurate statistics—this is Sudan, but I’ve worked here for three years, and I’ve never seen a case of Yellow Fever,” said Bushra Safia, a private physician in Khartoum, when we met in the city’s affluent Khartoum 2 district. “People know this, and so they don’t think it’s necessary.”

Several regions of Sudan actually have suffered from periodic flare-ups of the disease, which has killed hundreds in recent years and led the World Health Organization (WHO) to vaccinate up to 5 million people in war-torn Darfur. But it’s Sudan’s status as a strategic crossroads through which millions of migrants from higher-risk swathes of East and Central Africa pass, far more than its own health issues, that has prompted many countries to enforce this blanket insistence on Yellow Fever vaccinations.

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By this measure too, though, the trade in vaccination certificates threatens to have far-reaching implications. For such is the volume of foreigners seeking to buy certificates that Fathy, another dealer, who also declined to give his surname, has been able to maximize his profits by charging them up to four times (200 pounds/$32) the local price in order to facilitate their onward travel.

“For me, business is usually better when it’s hot,” he said between gulps of tea outside a public hospital where he works as a security official. “The foreigners in particular get tired, they don’t want to wait, and the system is automated so it’s difficult to jump the line.” He claims that he and his counterparts sell up to 250 cards a day during the peak period around the holy Muslim month of Ramadan, when many flee the stiflingly hot and conservative capital for more temperate climes.

Health officials, who’ve been assailed by budget cuts and are incapable of providing any services in many pockets of the country, are unsurprisingly keen to downplay the risk the trade poses.

“Sudan doesn’t really have a problem with Yellow Fever,” said Haidar Mohammed Ali, director of the National Medical Commission, outside of whose offices a cluster of card dealers intercept travelers and try to persuade them of the merits of forgoing the vaccination. “The problem is that we are at an intersection. For centuries people have come through here to get to Mecca (just across the Red Sea in Saudi Arabia), and they come with many diseases, so the international community believes that we are a risk.”

Local authorities are also at pains to point out that fake vaccination certificates are a global phenomenon. Officials at a Nigerian airport have been busted selling them, so too have their counterparts in South Sudan; polio vaccination workers in Pakistan, who have been routinely targeted by the Taliban, have had their work cut out battling forged cards as well.

But Sudan’s strategic location, high levels of corruption, and weakening economy, which has sent may of its citizens abroad in pursuit of work, have rendered its burgeoning new trade extra concerning.

Ahmed, the young dealer roving the streets of downtown, says he’s resorted to this because there are simply no alternative options: “There’s no work. I have nothing else to do.” For as long as he makes enough to pay off the police—who he claims have shaken him down for cash five times in the past two months—there appears to be little threat to his business. While Fathy, the hospital security official, insists that his low government wage of around 1,200 pounds a month ensures he has little choice but to supplement his income, even if that means contributing to a public health menace.

“Salaries are nothing; life here is expensive, so you’ve got to get by somehow, he said, before breaking off as a young man with a plane ticket to Dubai approached him. “I’ve got to work. I’ve got to go.”