Evaluating Large-scale Blood Transfusion Therapy for the Current Ebola Epidemic in Liberia

(See the editorial commentary by Colebunders and Cannon on pages 1208–10.) The ongoing Ebola virus disease (EVD) epidemic in West Africa is the largest ever recorded and has overwhelmed the healthcare systems in Sierra Leone, Liberia, and Guinea [1–4]. There are several promising vaccines and therapeutics under accelerated testing and production [3, 5], but they are not expected to become widely available for many months [6]. One of the only therapeutic methods immediately available and prioritized for evaluation by the World Health Organization (WHO) [7, 8] is blood transfusions from EVD survivors [9–12]. Convalescent patients have Ebola virus–specific antibodies in their serum that potentially facilitate recovery in acutely ill patients. This form of passive polyclonal antibody therapy has been used successfully to treat other infectious diseases [13], including cytomegalovirus infection, hepatitis B, rabies, respiratory syncytial virus infection, vaccinia, and varicella-zoster virus infection [14]. Convalescent transfusions are relatively simple, low cost, and scalable in low-income countries [7]. The evidence for their efficacy is limited but positive, including an 8-patient human study during a 1995 EVD outbreak in the Democratic Republic of the Congo [9], which reported a case-fatality rate of 12.5% under transfusion therapy and supportive care, and multiple animal studies [15]. Even minimally equipped medical settings can perform whole-blood transfusions, which require blood collection, blood grouping, testing for Ebola virus and several transfusion-transmittable diseases (human immunodeficiency virus infection, hepatitis B, and hepatitis C), and administration to critically acute patients [16]. Convalescent patients can donate blood starting 28 days following recovery as either convalescent plasma (CP) or convalescent whole blood (CWB) [16]. While CWB collection requires minimal equipment, CWB donation is physiologically demanding, and donors must wait 12–16 weeks between consecutive donations [16]. CP donation requires medical facilities that can separate the plasma and return the red blood cells [8], but the wait between CP donations is just 2 weeks, which increases the availability of treatments [16]. These facilities are not yet common in Africa [17], but international efforts are underway to bring the technology to hospitals in the affected countries. The WHO has advocated transfusion of convalescent specimens as the most promising of the available treatments for the ongoing West African epidemic [8, 16, 18]. Although mathematical models have been used extensively to investigate and design intervention measures for EVD [2, 19–25], none have addressed the challenges and impact of broad use of transfusion therapy. Here, we extend an established mathematical modeling framework [2] to assess scalability of transfusions and likely impacts on EVD incidence and mortality. Both the supply (convalescent survivors) and demand (hospitalized patients) are limited by Ebola hospitalization rates, which are perilously low in some regions and have become a major focus of international public health efforts.