Zaire ebolavirus
Deadliest Ebola species; the only one with licensed vaccines and treatments, ineffective against other species.
A different Ebola species is closing in on Zaire ebolavirus's death tolls: DR Congo's Bundibugyo outbreak reached 2,344 confirmed cases and 930 deaths by 20 July 2026, the third-largest Ebola epidemic on record after Zaire's own two largest.
Last refreshed: 31 July 2026 · Appears in 1 active topic
Why did Zaire Ebola get treatments in eight years while Bundibugyo still has none after 18?
Timeline for Zaire ebolavirus
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Pandemics and BiosecurityBackground
Zaire ebolavirus (EBOV) is the species behind the genus's highest-mortality and highest-profile outbreaks. First identified at Yambuku, DRC in 1976, it caused the 1995 Kikwit outbreak (315 cases, 81% case-fatality), the 2014-16 West Africa epidemic (28,616 cases, 11,310 deaths, the largest Ebola outbreak on record) and the 2018-20 Kivu outbreak in eastern DRC (3,481 cases, 2,299 deaths). Untreated case-fatality rates in healthcare settings run 50-90%.
It is the only Ebola species with licensed countermeasures. Merck's Ervebo vaccine (rVSV-ZEBOV) was used in ring vaccination during the Kivu outbreak and gained FDA approval in 2019; Regeneron's Inmazeb and Ridgeback's Ebanga, both monoclonal antibody treatments, followed in 2020 after the PALM trial cut treatment mortality below 12% at low viral loads. All three are species-specific and give no protection against Bundibugyo, Sudan or the genus's other recognised species.
That gap defines the 2026 medical-countermeasures paradox: tools built for Zaire over an eight-year development window from 2011 to 2020 do not exist for Bundibugyo, whose 2026 Ituri outbreak has been fought with the same supportive-care toolkit available in 1976.
A rival outbreak nears its record
By 20 July, DR Congo's Bundibugyo outbreak had reached 2,344 confirmed cases and 930 deaths, making it the third-largest Ebola outbreak of any species; WHO Director-General Tedros ranked it behind only Zaire ebolavirus's 2014-16 West Africa epidemic (28,616 cases, 11,310 deaths) and its own 2018-20 Kivu outbreak (3,481 cases, 2,299 deaths).
The comparison matters for Zaire's own record because it shows what a species-specific medical-countermeasures gap allows an outbreak to become: Zaire's Kivu epidemic was held under 3,500 cases with Ervebo ring vaccination and monoclonal antibodies, tools that did not exist for the eight Zaire outbreaks before it. Bundibugyo has no equivalent yet.