The 2013–2016 epidemic of Ebola virus disease, centered in West Africa, was the most widespread outbreak of the disease in history. It caused major loss of life and socioeconomic disruption in the region, mainly in Guinea, Liberia and Sierra Leone. The first cases were recorded in Guinea in December 2013; the disease spread to neighbouring Liberia and Sierra Leone, with minor outbreaks occurring in Nigeria and Mali. Secondary infections of medical workers occurred in the United States and Spain. Isolated cases were recorded in Senegal, the United Kingdom and Italy. The number of cases peaked in October 2014 and then began to decline gradually, following the commitment of substantial international resources.
It caused significant mortality, with a high case fatality rate. By the end of the epidemic, 28,616 people had been infected; of these, 11,310 had died, for a case-fatality rate of 40%. As of 8 May 2016, the World Health Organization (WHO) and respective governments reported a total of 28,646 suspected cases and 11,323 deaths (39.5%), though the WHO believes that this substantially understates the magnitude of the outbreak. On 8 August 2014, a public health emergency of international concern was declared and on 29 March 2016, the WHO terminated the Public Health Emergency of International Concern status of the outbreak. Subsequent flare-ups occurred; the epidemic was finally declared over on 9 June 2016, 42 days after the last case tested negative on 28 April 2016 in Monrovia.
The outbreak left about 17,000 survivors of the disease, many of whom report post-recovery symptoms termed post-Ebola syndrome, often severe enough to require medical care for months or even years. An additional cause for concern is the apparent ability of the virus to "hide" in a recovered survivor's body for an extended period and then become active months or years later, either in the same individual or in a sexual partner. In December 2016, the WHO announced that a two-year trial of the rVSV-ZEBOV vaccine appeared to offer protection from the variant of EBOV responsible for the Western Africa outbreak. The vaccine is considered to be effective and is the only prophylactic that offers protection; hence, 300,000 doses have been stockpiled. rVSV-ZEBOV received regulatory approval in 2019.
Epidemiology
Outbreak
The 2013–2016 outbreak, caused by the Ebola virus (EBOV), was the first anywhere in the world to reach epidemic proportions. Extreme poverty, dysfunctional healthcare systems, distrust of government after years of armed conflict, and the delay in responding for several months, all contributed to the failure to control the epidemic. Other factors, per media reports, included local burial customs of washing the body and the unprecedented spread of Ebola to densely populated cities.
It is generally believed that a one or two-year-old boy, later identified as Emile Ouamouno, who died in December 2013 in the village of Méliandou in Guinea, was the index case. His mother, sister, and grandmother later became ill with similar symptoms and also died; people infected by these initial cases spread the disease to other villages. These early cases were diagnosed as other conditions more common to the area and the disease had several months to spread before it became recognised as Ebola.
On 25 March 2014, the WHO indicated that Guinea's Ministry of Health had reported an outbreak of Ebola virus disease in four southeastern districts and that suspected cases in the neighbouring countries of Liberia and Sierra Leone were being investigated. In Guinea, a total of 86 suspected cases, including 59 deaths, had been reported as of 24 March. By late May, the outbreak had spread to Conakry, Guinea's capital—a city of about two million people. On 28 May, the total number of reported cases had reached 281, with 186 deaths.
In Liberia, the disease was reported in four counties by mid-April 2014 and cases in Liberia's capital Monrovia were reported in mid-June. The outbreak then spread to Sierra Leone and progressed rapidly. By 17 July, the total number of suspected cases in the country stood at 442, surpassing those in Guinea and Liberia. By 20 July, additional cases of the disease had been reported by the media in the Bo District, while the first case in Freetown, Sierra Leone's capital, was reported in late July.
As the epidemic progressed, a small outbreak occurred in Nigeria that resulted in 20 cases and another in Mali with seven cases. Four other countries (Senegal, Spain, the United Kingdom and the United States) also reported cases imported from Western Africa, which were quickly isolated and led to no other infections, with the exception of the US.
On 28 January 2015, the WHO reported that for the first time since the week ending 29 June 2014, there had been fewer than 100 new confirmed cases reported in a week in the three most-affected countries. The response to the epidemic then moved to a second phase, as the focus shifted from slowing transmission to ending the epidemic. On 8 April 2015, the WHO reported a total of only 30 confirmed cases, and the weekly update for 29 July reported only seven new cases.
Cases continued to gradually dwindle and on 7 October 2015, all three of the most seriously affected countries, per media reports, recorded their first joint week without any new cases. However, sporadic new cases were still being recorded, frustrating hopes that the epidemic could be declared over.
On 31 March 2015, one year after the first report of the outbreak, the total number of cases was over 25,000—with over 10,000 deaths. As the main epidemic was coming to an end in December 2015, the UN announced that 22,000 children had lost one or both parents to Ebola.
On 14 January 2016, after all the previously infected countries had been declared Ebola-free, the WHO reported that "all known chains of transmission have been stopped in Western Africa", but cautioned that further small outbreaks of the disease could occur. The following day, Sierra Leone confirmed its first new case since September 2015.
Countries that experienced widespread transmission
Guinea
On 25 March 2014, the WHO reported an outbreak of Ebola virus disease in four southeastern districts of Guinea with a total of 86 suspected cases, including 59 deaths. MSF assisted the Ministry of Health by establishing Ebola treatment centres in the epicentre of the outbreak. On 31 March, the U.S. Centers for Disease Control and Prevention (CDC) sent a team to assist in the response. Thinking that the spread of the virus had been contained, MSF closed its treatment centres in May, leaving only a skeleton staff to handle the Macenta region. However, in late August, according to media reports, large numbers of new cases reappeared in the region.
In February 2015, Guinea recorded a rise in cases; health authorities stated that this was related to the fact that they "were only now gaining access to faraway villages", where violence had previously prevented them from entering. On 14 February, violence erupted and an Ebola treatment centre near the centre of the country was destroyed. Guinean Red Cross teams said they had suffered an average of 10 attacks a month over the previous year; MSF reported that acceptance of Ebola education remained low and that further violence against their workers might force them to leave.
Resistance to interventions by health officials among the Guinean population remained greater than in Sierra Leone and Liberia, per media reports, raising concerns over its impact on ongoing efforts to halt the epidemic; in mid-March, there were 95 new cases, and on 28 March, and a 45-day "health emergency" was declared in five regions of the country. On 25 May, six persons were placed in prison isolation after they were found travelling with the corpse of an individual who had died of the disease. On 1 June, it was reported that violent protests in a north Guinean town at the border with Guinea-Bissau had caused the Red Cross to withdraw its workers.
In late June 2015, the WHO reported that "weekly case incidence has stalled at between 20 and 27 cases since the end of May, whilst cases continue to arise from unknown sources of infection, and to be detected only after post-mortem testing of community deaths". On 29 July, a sharp decline in cases was reported; the number of cases eventually plateaued at one or two cases per week in early August.
On 28 October, an additional three cases were reported in the Forécariah Prefecture by the WHO. On 6 November, a media report indicated Tana village to be the last known place with Ebola in the country, and on 11 November, WHO indicated that no Ebola cases were reported in Guinea; this was the first time since the epidemic began that no cases had been reported in any country. On 17 November, the last Ebola patient in Guinea had recovered, and was discharged from the hospital on 28 November. On 29 December 2015, the WHO declared Guinea Ebola-free.
On 17 March 2016, the government of Guinea reported that two people had again tested positive for Ebola virus in Korokpara. On 19 March, it was also reported by the media that another individual had died due to the virus at the treatment centre in Nzerekore, consequently, the country's government quarantined an area around the home where the cases took place. On 22 March, the media reported that medical authorities in Guinea had quarantined 816 suspected contacts of the prior cases; the same day, Liberia ordered its border with Guinea closed. On 29 March, it was reported that about 1,000 contacts had been identified, and on 30 March three more confirmed cases were reported. On 1 April, it was reported by the media, that possible contacts, which numbered in the hundreds, had been given an experimental vaccine using a ring vaccination approach.
On 5 April 2016, it was reported via the media, that there had been nine new cases of Ebola since the virus resurfaced, out of which eight were fatal; on 1 June, after the stipulated waiting period, the WHO again declared Guinea Ebola-free.
In September 2016, findings were published suggesting that the resurgence in Guinea was caused by an Ebola survivor who, after eight months of abstinence, had sexual relations with several partners, including the first victim in the new outbreak. The disease was also spread to Liberia.
Sierra Leone
The first person reported infected in Sierra Leone, according to media reports, was a tribal healer who had been treating Ebola patients from across the nearby border with Guinea and who died on 26 May 2014; according to tribal tradition, her body was washed for burial, and this appears to have led to infections in women from neighbouring towns. On 11 June Sierra Leone shut its borders for trade with Guinea and Liberia and closed some schools in an attempt to slow the spread of the virus; on 30 July the government began to deploy troops to enforce quarantines.
During the first week of November, reports told of a worsening situation due to intense transmission in Freetown. According to the Disaster Emergency Committee, food shortages resulting from aggressive quarantines were making the situation worse. On 4 November media reported that thousands had violated quarantine in search of food in the town of Kenema.
With the number of cases continuing to increase, an MSF coordinator described the situation in Sierra Leone as "catastrophic", saying, "there are several villages and communities that have been basically wiped out ... Whole communities have disappeared but many of them are not in the statistics." In mid-November, the WHO reported that, while there was some evidence that the number of cases was no longer rising in Guinea and Liberia, steep increases persisted in Sierra Leone.
On 9 December 2014 news reports described the discovery of "a grim scene"—piles of bodies, overwhelmed medical personnel and exhausted burial teams—in the remote eastern Kono District. On 15 December the CDC indicated that their main concern was Sierra Leone, where the epidemic had shown no signs of abating as cases continued to rise exponentially; by the second week of December, Sierra Leone had reported nearly 400 cases—more than three times the number reported by Guinea and Liberia combined. According to the CDC, "the risk we face now [is] that Ebola will simmer along, become native and be a problem for Africa and the world, for years to come". On 17 December President Koroma of Sierra Leone launched "Operation Western Area Surge" and workers went door-to-door in the capital city looking for possible cases. The operation led to 403 new reports of cases between 14 and 17 December.
According to the 21 January 2015 WHO Situation Report, the case incidence was rapidly decreasing in Sierra Leone. However, in February and March reports indicated another rise in the number of cases. The WHO weekly update for 29 July reported a total of only three new cases, the lowest in more than a year. On 17 August the country marked its first week with no new cases, and one week later the last patients were released. However, a new case emerged on 1 September, when a patient from Kambia District tested positive for the disease after her death; her case eventually resulted in three other infections among her contacts.
On 14 September 2015 Sierra Leone's National Ebola Response Centre confirmed the death of a 16-year-old in a village in the Bombali District. It is suspected that she contracted the disease from the semen of an Ebola survivor who had been discharged in March 2015. On 7 November 2015 the country was declared Ebola-free.
Sierra Leone had entered a 90-day period of enhanced surveillance that was scheduled to end on 5 February 2016, when, on 14 January, a new Ebola death was reported in the Tonkolili District. Before this case, the WHO had advised that "we still anticipate more flare-ups and must be prepared for them. A massive effort is underway to ensure robust prevention, surveillance, and response capacity across all three countries by the end of March."