Walter had one last chance to find the blood Francisca Akata so desperately needed: a small laboratory on the other side of the Atlantic. The modest size of the International Blood Group Reference Laboratory (IBGRL) in Filton, near Bristol in England, is misleading; the expertise at the IBGRL means it’s one of the world’s leading laboratories in rare blood identification.

If the donor and recipient are in different countries, the blood services of both countries will negotiate costs. The requesting country usually covers the cost of flying the blood in at 4°C, the temperature at which fresh red blood cells have to be preserved to keep them intact before transfusion.

“It’s generally a reciprocal agreement between countries so that no one who ever needs blood is penalised for being where they are,” Nicole Thornton, Head of Red Cell Reference at the IBGRL, told me. “Some countries charge a bit more per unit of blood, but there’s no hard and fast rule. Most don’t charge too much because they might be in the same situation at some point.” In the UK the charge is £125.23 per bag of blood.

Walter contacted Thornton, who searched the International Rare Donor Panel and identified 550 active O negative/Lutheran b negative donors worldwide. Because they are inherited, blood types tend to pool in specific populations, and 400 of those donors turned out to be in the UK – most of them in or around London. A flight from the UK to Cameroon would be much shorter than a flight from the USA. And the blood would be fresh.

As the blood was available, and because it wouldn’t make logistical sense to fly a second consignment if Francisca needed more than four units, the UK blood services agreed to send six bags of blood. All six UK donors who received a phone call and were able to donate did so within days.

In Rochester, Kent, England, it was James'* 104th donation. He first donated as an 18-year-old in the army in 1957, when he was told his O negative blood was “good for blue babies”. In 1985 he got a letter explaining his blood was rare (although not how rare) and asking if anyone in his family would donate so their blood could be tested. The family members he asked were reluctant, however, believing they “needed their blood for themselves”.

A few years later, in the early 1990s, James got his first phone call from the blood services, asking whether he would mind “popping down to the local hospital to donate blood for someone in Holland”. There, he was told that a taxi was waiting for his blood. He didn’t think this particularly unusual, saying that it was all in a day’s donation.

He wasn’t surprised to be called up again, but he didn’t know that his blood was going to Cameroon. And previously he hadn’t known he was Lutheran b negative, as well as O negative. He was surprised and mildly intrigued to learn that there were only 550 known people with the same blood in the world.

The bag of James’ blood joined the five bags from the other donors, and all six were couriered to Tooting in south London to start their 7000-km journey.

This was when Walter discovered how remote the hospital really was. Kumbo, in the mountains of north-west Cameroon, is more than 400 km north of both Douala and Yaoundé, the sites of the country’s major international airports. The blood would have to travel for several hours to get there, bumping over a dirt road in the March heat. Even packed in ice, it would be hard to keep it at the cell-preserving 4°C.

Francisca Akata’s blood landed at the international airport in Douala and was cleared through customs by noon on Friday 21 March 2014. A helicopter, supplied at the last minute by the hospital to avoid the lengthy road journey, was waiting outside. Her blood flew the rest of the way to Kumbo and arrived at 14.00, just after Francisca had been wheeled into the operating theatre.

The operation was a success, and the Catholic Diocese of Kumbo found her somewhere to recuperate before flying home. Walter still marvels at the efforts of so many people – on three separate continents – to save one life, “just like the shepherd who left 99 sheep and went after the one that was lost.”