CDC: DRC's Ebola outbreak hit 5,458 cases in its first 100 days, 7 times the 2014 pace

The first 100 days after an Ebola outbreak is identified are the window in which transmission dynamics, the impact of early interventions, and the likely trajectory all become legible. A Notes from the Field report in the US CDC's Morbidity and Mortality Weekly Report, published on 24 September, uses that window to place the current Democratic Republic of the Congo outbreak against four predecessors — and the comparison is stark.

During the current outbreak's first 100 days, May 14–August 21, 2026, the DRC reported 5,458 confirmed cases and 2,606 (48%) deaths [s1]. The report states this represents 7 and 16 times as many cases as the 2014 West Africa and 2018 DRC outbreaks, respectively, recorded during their own initial 100-day periods [s1].

The five outbreaks, at the same point in their lives

The comparison is what gives the 5,458 figure meaning. Ebola outbreaks are usually small at day 100, and the two previous Bundibugyo virus events were.

The 2007 Uganda Bundibugyo outbreak had fewer than 50 cases identified during its first 100 days; it ultimately reached 131 confirmed, probable, and suspected cases and 42 (32%) deaths [s1]. The 2012 DRC Bundibugyo outbreak likewise had fewer than 50 cases in its first 100 days, and totalled 62 cases and 34 (55%) deaths [s1].

The two large Zaire ebolavirus outbreaks were bigger but still far behind 2026. During the first 100 days of the 2014 West Africa outbreak (March 23–July 1, 2014), 759 suspected, probable, or confirmed cases and 467 (62%) deaths were documented [s1]; that outbreak eventually reached 28,610 cases and 11,308 (40%) deaths [s1]. During the first 103 days of the 2018 DRC outbreak (August 1–November 11, 2018), there were 295 confirmed cases, 38 probable cases, and 171 (51%) deaths [s1], with an eventual total of 3,470 cases and 2,287 (66%) deaths [s1].

Set those against the 2026 outbreak's 5,458 confirmed cases and 2,606 deaths at day 100, and the scale of what is unfolding in the DRC is clear: this Bundibugyo epidemic has, in its opening months, already behaved like nothing in the recorded history of the species that causes it.

Why Bundibugyo is the hard case

The species is the problem. Bundibugyo virus is one of the three Ebola viruses known to cause large outbreaks [s2]. But while there are licensed vaccines and therapeutics for Ebola virus disease caused by Zaire ebolavirus, there is no approved vaccine or treatment for other Ebola diseases, including Bundibugyo virus disease [s2]. The two tools that bent the curve in the DRC's recent Zaire-species outbreaks — a licensed vaccine and monoclonal therapeutics — are simply not available here.

That absence is visible in the case-fatality figures. WHO puts the average Ebola case-fatality rate at around 50%, with past outbreaks ranging from 25% to 90% [s2]. The 2026 outbreak's 48% at day 100 sits squarely in that band — which, for a virus with no approved countermeasures, is what an unmitigated epidemic looks like rather than a reassuringly low number.

What the 100-day lens is and is not

The report is explicit that the first 100 days are a forecasting tool, not a verdict. Early trajectory shaped by case-finding intensity and reporting completeness can over- or under-state the eventual course, and the 2014 comparison cuts both ways: that outbreak's day-100 count of 759 gave little hint of the 28,610 it would reach. A fast start can be outrun by an even faster middle, or blunted by a response that finally gets ahead of it.

What the lens does establish is relative severity, and on that measure 2026 is already an outlier. A Bundibugyo outbreak that at day 100 has 7 times the cases of West Africa and 16 times the cases of the 2018 DRC epidemic is not a normal event for the species, and it is accumulating that toll without the vaccine and treatment that shortened the last two large Congolese outbreaks.

What to watch

The number that matters next is whether the daily case count has peaked or is still climbing past day 100. Day-100 figures freeze a moving epidemic; the trajectory after that point — and whether countermeasure trials for non-Zaire species can be stood up at speed — is what will decide how far beyond 5,458 this outbreak runs.

Sources

• Notes from the Field: The First 100 Days of Five Ebola Outbreaks — DRC, Uganda, and West Africa, 2007–2026 — MMWR (CDC), 24 September 2026
• Ebola disease (fact sheet) — World Health Organization