UPDATE: Just one day on from the publication of this article, the World Health Organisation has confirmed a new case of Ebola as the cause of a death in Sierra Leone.

AS OF January 14th 2016, the World Health Organisation (WHO) has declared the west African country of Liberia free of Ebola. Along with it, Africa as a whole is now clear of the killer virus. The outbreak that ravaged the region over the course of the last two years was the worst the world has ever seen. The first reported case dates back to December 2013, in Guéckédou, a forested area of Guinea near the border with Liberia and Sierra Leone. Travellers took it across the borders: by late March 2014, Liberia had reported eight suspected cases and Sierra Leone six. By the end of June that same year 759 people had been infected and 467 people had died from the disease. To date, 28,637 cases and 11,315 deaths have been reported worldwide, the vast majority of them in these same three countries.

The extremely high mortality rate of the disease, estimated at around 60% in this outbreak, means that Ebola can quickly claim more lives than other, more established killers. The rate at which cases give rise to subsequent cases, which epidemiologists call R0, is the key variable in the spread of Ebola. For easily transmitted diseases R0 can be high; for measles it is 18. Ebola is much harder to catch: estimates of R0 in different parts of the outbreak range from 1.5 to 2.2. Any R0 above 1 is bad news.

But now the outbreak has finally been halted, though it has been a very slow process to stop the last transmissions. Guinea was declared Ebola-free on December 29th 2015 and Sierra Leone has been free of the disease since November 7th. Liberia was the first of the three countries to be declared Ebola-free on May 9th 2015, however the virus subsequently re-emerged in late June and then again around the 22nd of November, on that occasion resulting in three confirmed cases and one death. January's declaration of eradication is the WHO's third for the country, demonstrating how vigilant everyone still needs to be to avoid future flare-ups. The chart above shows numbers from both the WHO's regular situation reports and from patient databases (which tend to be more accurate but are less complete for more recent weeks).