If you head over to the main History of Vaccines site, you’ll see that we have an Articles section where information on the known vaccine-preventable diseases is posted. In the last few years, two more vaccines have been authorized for use against their respective diseases: Ebola and Coronavirus. In this blog post, you will get a preview of the information that will soon be posted on Ebola, albeit in a slightly different format than it is on the Articles section.
In 1976, two outbreaks of a hemorrhagic fever disease in Zaire (now the Democratic Republic of the Congo) attracted the attention of world public health experts because of the novelty of the disease and the unknown nature of what was causing the disease. The epidemic was detected when a 42-year-old man sought care at the Yambuku Mission Hospital. He had traveled north from Yandongi Village, consuming diverse types of meats along the way. Initially, physicians treated him for malaria, which is common there and matched his symptoms. However, after a few weeks of continued decline in his health, he passed away. Unfortunately, the hospital was also the point of care for pregnant women and others in that part of the country, with many people traveling great distances to receive care. Part of that care included injections of medication. With sterile supplies not being available, many people were exposed to the medical equipment used in the initial (index) case and used on another man who sought care for similar symptoms.
What resulted was the first large and sustained epidemic of Ebola Hemorrhagic Fever (EHF; or Ebola Virus Disease, EVD) in recorded history. Healthcare workers at the Yambuku Mission Hospital also became ill. Local health authorities sought help from national authorities. Faced with the growing epidemic that did not seem to respond to any treatment, national authorities contacted international health agencies. By the time the epidemic was brought under control through strict isolation and quarantine measures, 318 cases were identified with 280 deaths reported (a case-fatality rate of 88%).
That same year, another epidemic with all the markings of EHF appeared in Sudan, northeast of Zaire. In that epidemic, 284 cases with 151 deaths (53% case-fatality rate) were reported. Like the epidemic in Zaire, international response was requested and provided. Part of that response included the search for what was causing the disease. For that, teams of scientists around the world received blood and tissue samples from patients.
By 1977, after a concerted effort to identify the pathogen, scientists declared the discovery of a new virus named Ebola after the river in Zaire where the first cases were identified. They discovered the virus through different techniques including attempts to grow the virus in the laboratory, using electron microscopes to see the virus, and attempts at cross-reacting antibodies against known hemorrhagic fever virus (like Marburg virus).
Other epidemics of EHF have happened from time to time in different parts of Africa. Cases of the disease were also detected in travelers to other countries, though they never triggered epidemics in those places they visited. Or there were laboratory accidents and/or cases of Ebola infection in animals and not people without an actual epidemic. One such incident was that of an outbreak of Ebola infections in research monkeys in Reston, Virginia. In 1989, macaque monkeys brought to Virginia for medical research tested positive for Ebola after exhibiting signs and symptoms of the infection, with many of them dying. Several of the handlers also tested positive for the virus, but it was not the same Ebola virus that caused the outbreaks 13 years earlier in Zaire. The virus — now known as Ebola Reston — was a form of Ebola that can infect humans but not cause severe disease.
In 2014, an outbreak of Ebola centered around Guinea, Liberia and Sierra Leone in West Africa caused about 30,000 cases and 11,300 deaths. To date, it was the biggest outbreak of Ebola in recorded history, with cases traveling out of the area and being detected in 7 other countries in Europe and North America. By 2016, the epidemic was brought under control through international collaboration and delivery of medical supplies and manpower. The overall death rate from this epidemic was lower than that of previous epidemics as healthcare providers improved their treatment methodologies and newer medications and medical technologies were available.
In 2019, the Food and Drug Administration approved an Ebola vaccine for use in people 18 years of age and older who are responding to an epidemic, working in the laboratory with Ebola virus, or healthcare personnel at a facility treating suspected and/or confirmed Ebola patients. The vaccine was the result of decades of research that started almost immediately after the first samples of Ebola Zaire arrived at different laboratories in 1976. One of the field clinical trials was done during the 2014–2016 epidemic in West Africa. According to the Centers for Disease Control and Prevention:
“Clinical efficacy of the vaccine was supported by a randomized cluster (ring) vaccination study during the 2014–2016 outbreak in Guinea. In this study, 3,775 people in close contact with diagnosed EVD cases (contacts) and their close contacts (contacts of contacts) received immediate vaccination. No one who was vaccinated immediately developed EVD 10 or more days after vaccination.”
History of Ebola Virus Disease, Centers for Disease Control and Prevention: https://www.cdc.gov/vhf/ebola/history/summaries.html
25 years ago in Virginia, a very different Ebola outbreak, CBS News: https://www.cbsnews.com/news/25-years-ago-in-virginia-a-very-different-ebola-outbreak/
2014-2016 Ebola Outbreak in West Africa, Centers for Disease Control and Prevention: https://www.cdc.gov/vhf/ebola/history/2014-2016-outbreak/index.html