SUMMARY
There were 2 confirmed cases of Ebola virus disease (EVD) reported in the week to 2 August: 1 in Guinea and 1 in Sierra Leone. This is the lowest weekly total to have been reported since March 2014, and marks a third consecutive decline in weekly case incidence. This decline is underpinned by continued refinements to all elements of the response. In particular, strengthened capacity for contact tracing and case investigation has increased confidence that the few remaining known chains of transmission are better understood and controlled than was the case several months ago. Maintaining these resources in the months ahead will be critical, as there remains a significant risk of further transmission and an increase in case incidence in the near and medium term. Almost 2000 contacts remain under observation across 5 prefectures in Guinea and 4 districts in Sierra Leone, and despite intensive efforts a small number of contacts in both countries have not been traced or have been lost to follow-up. In addition, recent high-risk transmission events in Guinea and Sierra Leone are very likely to result in further cases in the coming weeks.
Illustrating the continuing challenges, the single case reported from Guinea is a contact who was lost to followup, and who is likely to have generated a substantial number of further high-risk contacts. The case, a 28-yearold woman, is a registered contact associated with a known chain of transmission that has given rise to several generations of cases in the Ratoma area of the capital, Conakry, over the past several weeks. After being lost to follow-up the case travelled south from Conakry through Forecariah and into Kambia, Sierra Leone, where she reportedly visited a traditional healer, before returning to Ratoma via Forecariah. Intensive efforts are underway to identify and trace all contacts in Guinea and Sierra Leone. 1080 contacts remain under follow-up in 5 western prefectures in Guinea, with the vast majority (>90%) of contacts located in Conakry and Forecariah.
An interim analysis of the Ebola ça suffit! ring vaccination trial in Guinea suggests that the investigational rVSVZEBOV Ebola vaccine protects people exposed to EVD. The trial will continue in Guinea, with all rings around confirmed cases now receiving immediate vaccination. Previously, rings were randomly allocated to receive either immediate vaccination or vaccination 21 days after the confirmation of a case.
No new cases were reported from Liberia in the week to 2 August. All contacts have now completed their 21-day follow-up period. The last case was discharged after testing negative for EVD for a second time on 23 July.
In Sierra Leone, the case reported this week is one of over 600 contacts generated by the single case reported in Tonkolili the previous week (the index case). The new case is a family member who provided care to the index case. Over 40 contacts are considered to be at high risk of infection because of the nature of their contact with the index case, and there is a high probability that further cases will arise. Investigations into the source of infection of the index case, who is thought to have acquired infection in Freetown before traveling to Tonkolili, are still ongoing. Across the country a total of 811 contacts remain under follow-up, with the vast majority located in Tonkolili. All contacts associated with known chains of transmission in Kambia have now completed the 21-day follow-up period, although intensive efforts are underway to identify any contacts associated with the case reported from Ratoma, Guinea, in the week ending 2 August.
For the first time in 3 weeks, no health worker infections were reported from any of the affected countries. There have been a total of 880 confirmed health worker infections reported from Guinea, Liberia, and Sierra Leone since the start of the outbreak, with 512 reported deaths