The Democratic Republic of Congo is in the middle of its deadliest Ebola outbreak ever, and nobody has a vaccine for it. Bundibugyo ebolavirus is driving this outbreak — a strain distinct from the Zaire virus that caused every major outbreak from 2014 to 2020. As of August 5, there are 3,994 confirmed cases and 1,803 deaths — a 45% fatality rate. WHO Director-General Tedros Adhanom Ghebreyesus flew to Kinshasa today, his second visit since WHO declared the outbreak in May, and called on the world to "urgently and massively scale up" the response. The central fight isn't just about resources. It's about what the tools actually are.

1. Wait for the Right Vaccine (WHO, Merck)

An imperfect vaccine could do more harm than good, and better options are already in trials.

Ervebo wasn't built for this virus. On May 28, WHO experts formally recommended against using Ervebo — the licensed vaccine that stopped the 2018–20 Kivu outbreak — outside of controlled research settings. Ervebo targets Zaire ebolavirus, not Bundibugyo. The WHO judged evidence of cross-protection "limited and inconclusive." Deploying it widely could create false security and undermine other control measures. If vaccinated people later got infected, public confidence in vaccines could collapse in a country where trust is already fragile.

Three Bundibugyo-specific vaccines just entered trials. IAVI, Moderna (mRNA-1469), and Oxford all started expedited trials through a protocol called PARTNERS. The UK trial launched July 24; Moderna's Phase 1 started in Canada. Dr. Vasee Moorthy, WHO's acting lead of R&D Blueprint, said clearly there are "still no proven safe and efficacious treatment, preventive or vaccination options for the Bundibugyo species." WHO also recommended three candidate treatments — remdesivir, MBP-134, and maftivimab — and all three are now in trials in Ituri province. The right tools are coming; the question is whether waiting for them is acceptable.

2. But Ervebo Could Work Right Now (Isaac Bogoch, University of Toronto; Jean-Jacques Muyembe-Tamfum, DRC)

The cross-protection signals are real, the deaths are real, and waiting months is its own kind of decision.

The evidence for cross-protection is more than noise. Lab studies show Ervebo triggers cross-protective antibodies against Bundibugyo in some individuals. Animal studies from a decade ago showed increased survival in primates. In the current outbreak: among 242 documented fatal cases, none had prior Ervebo vaccination. Nine vaccinated individuals survived infection. This is anecdotal — but it's the kind of signal researchers say demands a clinical trial.

Controlled Ervebo trials should start now. Isaac Bogoch at the University of Toronto says WHO should run parallel trials of the licensed vaccine now — "particularly given its immediate availability." Edouard Lhomme at the University of Bordeaux put it bluntly: "this question should no longer be debated, it should be tested in a carefully designed prospective clinical study." Jean-Jacques Muyembe-Tamfum — DRC's leading Ebola researcher — co-authored a Lancet article arguing that if the cross-protection signals are real, "decisions made during this outbreak might be remembered not only for the evidence they generated, but also for the lives they could help save."

Ring vaccination also runs into a structural problem here. Bogoch points out that the strategy that worked in Kivu depends on contact tracing, and most cases in this outbreak are surfacing only after death. Even a perfect Bundibugyo-specific vaccine won't help if you can't find people to vaccinate.

3. And the Ground Response Is Already Failing (Africa CDC, MSF)

The vaccine debate may not matter if responders can't reach patients in the first place.

Contact tracing has broken down. The International Rescue Committee found that tracers are reaching only 20% of contacts in the tracing system. Between 60 and 70% of new cases are appearing outside any monitored contact network. Jean Kaseya, director-general of Africa CDC, said it plainly at a July 22 summit: "People are dying because there are no vaccines, no medicine and no funding."

The structural problems run deep. The outbreak's epicenter, Ituri province, is an active conflict zone. Armed groups control significant territory in Ituri and the Kivu provinces, blocking responders. Health workers in Ituri are striking over unpaid wages, making case detection and care worse. MSF's John Johnson, the organization's medical lead for epidemic response, said community engagement is essential but "none of this is effective" in a conflict zone without sustained trust-building. MSF has also flagged a shortage of PCR diagnostic kits that "considerably slows down case confirmation."

The outbreak has infected 75 healthcare workers and killed 17 of them. That puts the response system itself at risk.

Where This Lands

WHO is betting that deploying an unproven vaccine now could damage public trust in ways that outlast this outbreak, and that Bundibugyo-specific vaccines — months away from the outbreak zone — are the right call. The researchers pushing for Ervebo trials aren't asking for a mass rollout; they want controlled clinical trials that generate real evidence while the right vaccine gets built. Africa CDC and MSF are pointing at something both camps may be underestimating: the ground-level response has already come apart, and no vaccine strategy works if responders can't find the patients. The US has committed over $512 million to the effort. The WHO chief is in Kinshasa today. The death toll exceeded 1,000 by July 22 — the fastest any Ebola outbreak has ever reached that milestone.

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