WHEN Adama Sankoh, the last person known to have Ebola in Sierra Leone, was discharged from hospital on August 24th the medical clock began ticking: if no one else contracts the disease in the next 42 days, the country can be deemed free of it. But like most infectious outbreaks, this one forms a bell curve when charted over time. The right-hand tail of the curve has stubbornly refused to disappear, as the occasional case keeps popping up.

What is most striking is that this long tail is mainly due to the disease lingering on in the country’s north-west. By contrast its south-east has been free of the scourge for nearly six months. Yet the north-west has had far more foreign aid.

One reason for the south-east’s success is that it is more isolated. (Traffic between the north-west and Freetown, the capital, is a lot heavier.) But subtler factors, including the influence of prominent locals, may deserve more credit.

It was in the east of Sierra Leone, near its border with Guinea, that Ebola first took hold in the country, in around April 2014. At Kenema Government Hospital, the biggest in the south-east, two respected doctors, Sheik Umar Khan and Mohamed Vandi, immediately sought ways to fight the disease. As personal doctors to Amara Vangahun, the paramount chief of Kenema town, they persuaded him to call an urgent meeting. The gathering included other paramount chiefs, imams, priests and political leaders such as the mayor. Under Dr Vandi’s guidance the group passed 30 laws, for instance banning families from taking in visiting relatives who might be sick. For failing to report a guest, you could be fined or jailed.

At first the bell curve still swooped upwards. Health workers often lacked protective gear, ambulances were scarce and villagers did not realise how dangerous Ebola was. But their doubts dwindled as the deaths mounted. They recognised the full horror when Dr Khan died on July 29th.

After Ebola reached a climax in mid-August it began to plummet in the east, well before much foreign aid had materialised. Meanwhile the contagion spread westward across the country. When it hit Port Loko in the north-west, that district’s health managers took charge, along with a politically appointed Ebola co-ordinator. They brushed non-medical people aside, ignoring chiefs and headmen, who often felt insulted. (Northerners, many from the Temne tribe, have a longstanding reputation for rebelliousness.) Medical officials also clashed with traditional healers loth to refer the sick to hospitals. The flood of donations from foreign governments and agencies in some respects made matters worse, as factions vied for vehicles, food and cash. Western-led aid agencies also jockeyed for access to the rush of funds.