I am glad that Nigeria is officially free of Ebola now. The story is reassuring. New outbreaks of Ebola are stoppable. But the numbers are sobering. They show how far gone the situation is in West Africa.
The index patient (as the source of the outbreak is known) arrived in Lagos, a megacity of 21 million people, on July 20th — a recipe for disaster. Over the next six weeks 19 further people were diagnosed with Ebola. The death toll was eight people, many of them health workers. Those infected generated 989 contacts, and it took 18,500 in-person, follow up visits to make sure that the virus did not spread further.
Translate those ratios to West Africa, where the latest WHO situation report shows there were 2,638 new cases between September 26 and October 17. In Nigeria, each infected person on average generated 50 contacts, and each contact generated 18 follow-up visits. This is only the roughest of ballpark estimates, but if the ratios were similar, it means that solving the spread in Liberia, Sierra Leone, and Guinea would generate 130,000 contacts and require 2.4 million follow-ups in the next three weeks. By mid November that will double. Obviously things [...]