Ebola Returns Yet Again—Understanding and Controlling a Deadly Disease

Microscopic image of the Ebola virus

Abram Wagner, MPH '12, PhD ’15

Research Fellow and Lecturer, Epidemiology

Since its emergence in central Africa over 40 years ago, Ebola has captivated scientists and the general public alike. Media descriptions of sudden outbreaks in distant lands with the infected dying in large numbers from profuse bleeding have shocked and frightened the US public. Success in developing pharmaceuticals was elusive, and governments and industry in wealthy Western countries were slow and sometimes unwilling to contribute control efforts.

Ebola outbreaks surfaced periodically in Africa in the latter half of the 20th century, but the devastation wrought by Ebola in West Africa in 2013-2016 brought this deadly disease back to the forefront for the Western public, with many wondering, "Why don't we have an effective treatment or preventive therapy as we do for so many other infectious diseases?"

Rapid urbanization, increased travel across borders and regions, and inadequate medical and public health infrastructure made West Africa an Ebola powder keg.

The 2013 outbreak showed both the limits of modern medicine and the success of traditional epidemiological tools in countries facing dramatic demographic changes. With rapid urbanization, increased travel across borders and regions, and inadequate medical and public health infrastructure, West Africa was a veritable Ebola powder keg. Deep-rooted cultural practices—like direct contact with dead bodies in funeral preparations—exacerbated the spread of disease, and medical doctors found themselves without effective medical treatments. At the same time, traditional public health interventions had some success. For example, many wondered why Liberia was so devastated by disease but Nigeria, a hub of travel for the region with huge urban slums, was not. One potentially important reason was that, unlike Liberia, Nigeria rapidly employed traditional epidemiological tools such as contact tracing—where epidemiologists find recent contacts of a case to connect them with doctors as needed and isolate them if they develop disease.1

Several new Ebola vaccines had been in the pipeline prior to this outbreak. However, progress was slow and many Western pharmaceutical companies simply gave up on development efforts given the vaccine was unlikely to be profitable since it would be used in mostly poor rather than high-income countries (an oft-repeated pattern—the quest for a hepatitis E vaccine was stopped by Western research institutions in the 1990s).2 One Ebola vaccine candidate was promisingly effective in a population from the United States,3 but was abandoned after scientists realized that most Africans already had immunity to the specific adenovirus strain (serotype 5) that was used as a base to add on Ebola proteins and therefore the vaccine had lower probability of being useful in the area of the world where the need was greatest.4

In the face of Ebola’s human wreckage, the best in humanity emerged and placed the focus directly on the need for rapid vaccine development.

Ironically, in the face of Ebola's human wreckage, the best in humanity also emerged and placed the focus directly on the need for rapid vaccine development. Researchers were able to compress the implementation of certain clinical trials, typically a process that takes several years, into just a single year.5 The WHO formalized the Ebola response model to provide a blueprint for rapid mobilization of pharmaceutical resources in response to the next emerging infectious disease outbreak.6 The Coalition for Epidemic Preparedness Innovations was launched to incentivize development of vaccines against pathogens we currently know and those we don't but that may emerge in the future.7

Ebola is once again in news headlines around the world. Public health officials are cautious in their assessment of this more recent appearance of Ebola—with over 200 cases from two outbreaks within the Democratic Republic of Congo (DRC) since 2017.8 We now have Ebola vaccines, and international teams have been deployed to Central Africa in an attempt to limit the spread of disease through the use of ring vaccination, in which close contacts of Ebola cases are targeted for vaccination.

Challenges in the distribution of vaccines in Africa remain in routine immunization and for mass vaccination campaigns.

Yet this outbreak has presented us with a new set of challenges, especially given that the outbreaks have been geographically situated in the middle of a civil conflict.9 Immense challenges in the distribution of vaccines in Africa remain both in routine immunization and for mass vaccination campaigns with vaccines that theoretically should be standard. Deploying Ebola vaccines has required the use of outside organizations, which have provided critical financing, labor, and safe vaccine transport. It's currently unknown whether these measures will result in lasting change beyond this outbreak. The DRC has received additional funding from international organizations to boost routine vaccination programs in certain provinces,10 but this vaccination drive is relatively isolated and only occur in one of two provinces affected by the current Ebola outbreak.

Control of the spread of Ebola may continue to prove elusive despite new insights into how it can be transmitted. Ebola can be spread not only through blood but also by semen11 and breast milk,12 including months after a person recovers from disease. That we have only recently discovered that people with Ebola, after recovering from acute disease, can still potentially transmit infection months later is a testament to how little we still know about this disease. While medical advances will certainly aid us in our effort to combat Ebola, traditional epidemiological tools will remain essential to stopping spread of this deadly disease.


1. World Health Organization. Ebola situation assessment. 2014.

2. Labrique et al. Hepatitis E, a vaccine-preventable cause of maternal deaths. Emerg Infect Dis. 2012;18: 1401-1404.

3. Ledgerwood et al. A replication defective recombinant Ad5 vaccine expressing Ebola virus GP is safe and immunogenic in healthy adults. Vaccine. 2010;29(2): 304-313.

4. Abbink et al. Comparative Seroprevalence and Immunogenicity of Six Rare Serotype Recombinant Adenovirus Vaccine Vectors from Subgroups B and D. J Virol. 2007;81(9): 4654-4663.

5. Kieny. Lessons learned from Ebola Vaccine R&D during a public health emergency. Human Vaccines & Immunotherapeutics. 2018;14(9): 2114-2115.

6. World Health Organization. R&D Blueprint. 2016.

7. Røttingen et al. New vaccines against epidemic infectious diseases. N Engl J Med. 2017;376: 610-613.

8. World Health Organization. Ebola situation reports. 2018.

9. Editorial team. DR Congo: managing Ebola virus in war. Lancet. 2018;392: 1280.

10. Gavi The Vaccine Alliance. DRC launches major vaccination drive. 2018.

11. Deen et al. Ebola RNA Persistence in Semen of Ebola Virus Disease Survivors — Final Report. N Engl J Med. 2017;377: 1428-1437.

12. Sissoko et al. Ebola Virus Persistence in Breast Milk After No Reported Illness: A Likely Source of Virus Transmission from Mother to Child. Clin Inf Dis. 2017;64(4): 513-516.

About the Author

Abram WagnerAbram Wagner studies predictors of vaccine-preventable disease, with a focus on vaccine hesitancy. It has been said that we are living in the “platinum age of vaccinology,” as advances in genetic engineering and immunology have expanded the scope of vaccine development to prevent a greater array of diseases than previously thought possible. Since 2000, the US has licensed ten new vaccines and, at the same time, has seen the unfortunate emergence of widespread vaccine hesitancy leading to outbreaks of measles and pertussis. Vaccine hesitancy has primarily been studied in high-income countries and is poorly researched in settings like China, even though we are living in a globalized age where both news and infections have the potential to rapidly spread around the world. The long-term goals of Wagner’s research are to characterize the pathways between public health messaging and the incidence of vaccine-preventable diseases.

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