For many people, the 2014-2016 Ebola outbreak was the first time they had heard of Ebola virus disease. It was not the first outbreak of the disease, but it was the largest, with approximately 28,500 suspected cases. Now, in 2016, the epidemic has ended1. However, it is only a matter of time before Ebola emerges again. If a vaccine were to be developed and widely distributed before the next outbreak, it could save many lives.
To create an effective vaccine, it is important to understand how natural infection affects immunity. Little is known about this in the case of Ebola virus disease, so a recent study examined antibodies from survivors of Ebola virus disease or Marburg disease.
Antibodies are an important part of your immune system. These Y-shaped proteins bind to infectious agents, such as viruses and bacteria. This binding prevents the infectious agents from entering your cells and causing damage, and also makes them targets for other cells of the immune system to destroy2.
Antibodies are highly specific for what they will bind to. Antibodies that are produced from an infection caused by one infectious agent will likely not bind to a different infectious agent. For example, antibodies generated in response to an infection by Ebola virus will not bind to Zika virus. Instead, your immune system has to produce new antibodies specific to this different infectious agent2.
However, if the infectious agents are closely related to each other, sometimes antibodies will react to both. This is called cross-reactivity. Cross-reactivity can result in protection from both diseases; however, this is not always true. Antibodies that can cross-react might not be numerous enough to prevent the new infectious agent from causing disease3.
Knowing if antibodies will cross-react is an important question with regards to Ebola virus disease. There are currently five known species of Ebolavirus. Each species causes hemorrhagic fever, but some species are more lethal than others4. There is also Marburg virus, which is in the same family as ebolaviruses and also causes hemorrhagic fever5. If antibodies can bind to multiple species of Ebolavirus, or even Marburg virus, there is the possibility that the person might be protected against these other species.
Researchers found that in survivors of Ebola virus disease, antibodies did cross-react to other species of Ebolavirus. In addition, the antibodies from survivors of Ebola virus disease interacted with Marburg virus, and the antibodies from survivors of Marburg virus disease interacted with ebolaviruses6.
The study also confirmed another important finding about the lifespan of the antibodies directed against ebolaviruses. After an infection, your body will continue to produce antibodies to protect you from further infection. However, this only continues for a certain amount of time2.
It has been previously shown that antibodies directed against ebolaviruses are long-lived, and the results of this new study were in line with those previous findings. One group of Ebola virus survivors that participated in the study were infected in an outbreak of Sudan ebolavirus, a species of Ebolavirus. Fourteen years after the outbreak, the survivors still had detectable antibodies. Another group in the study had detectable antibodies seven years after infection6.
Knowing this can help researchers in developing a vaccine against ebolaviruses. Natural infection produced cross-reactive antibodies against ebolaviruses, which means that a vaccine could potentially generate cross-reactive antibodies as well. This, then, could potentially translate into protection against multiple species of Ebolavirus. Additionally, a vaccine might protect people against ebolaviruses for a long time, as survivors of Ebola virus disease had long-lasting antibodies.
The race is on to create a vaccine before the next outbreak of Ebola virus disease. New findings in the coming months and years can help to make that vaccine more effective.
This blog post is based off an original research article. You can read the original research article for free here.
1: Ebola (Ebola virus disease): 2014-2016 Ebola outbreak in West Africa [Internet]. 2016. Atlanta (GA): Centers for Disease Control and Prevention; [cited 2016 Nov 2]. Available from http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/index.html
2: Parham P. 2015. The immune system. 4th ed. New York: Garland Science, Taylor & Francis Group. Chapter 4, Antibody structure and the generation of B-cell diversity; p 81-112.
3: Frank SA. 2002. Immunology and evolution of infectious disease. Princeton (NJ): Princeton University Press. Chapter 4, Specificity and cross-reactivity. Available from https://www.ncbi.nlm.nih.gov/books/NBK2396/
4: Laupland KB, Valiquette L. 2014. Ebola virus disease. Can J Infect Dis Med Microbiol. 25(3):128-9.
5: Media centre: Marburg haemorrhagic fever [Internet]. 2012. World Health Organization; [cited 2016 Nov 2]. Available from http://www.who.int/mediacentre/factsheets/fs_marburg/en/
6: Natesan M, Jensen SM, Keasey SL, Kamata T, Kuehne AI, Stonier SW, Lutwana JJ, Lobel L, Ulrich RG. 2016. Human survivors of disease outbreaks caused by Ebola or Marburg virus exhibit cross-reactive and long-lived antibody responses. Clin Vaccine Immunol. 23:717-24.