Frontline health workers in eastern Democratic Republic of Congo may soon be offered an experimental vaccine regimen against the Bundibugyo strain of Ebola, as researchers test whether it can provide partial protection while a strain-specific vaccine remains months away.Health officials are laying the groundwork for a study to test whether Merck & Co.’s licensed Ebola vaccine, Ervebo — which targets the more common Zaire strain — followed by an experimental vaccine being developed against Sudan Ebola, can generate an immune response that provides at least some protection against Bundibugyo.Africa Centres for Disease Control and Prevention is working with Médecins Sans Frontières and other partners on the design of a small study that it expects to submit to its executive committee for clearance Tuesday. The trial could begin within two weeks if it receives regulatory and ethical approval, the Addis Ababa-based agency said in an email Sunday.At least 121 health workers and other frontline responders have been infected during the outbreak. Eighteen are hospitalized, and 36 have died, underscoring the urgency of finding ways to protect them while Bundibugyo-specific vaccines remain in development.“Africa CDC recognizes the urgency of protecting healthcare workers and supports a timely process that maintains participant safety and scientific integrity,” it said. “We intend to do this under a phase-2 clinical trial among a small cohort of healthcare workers, where any level of protection could provide benefits to them.”The proposal highlights an ongoing debate over whether existing Ebola vaccines that weren’t designed for Bundibugyo might nevertheless offer enough cross-protection to benefit frontline workers while strain-specific vaccines remain months away.Arthur Caplan, founding head of the division of medical ethics at NYU Grossman School of Medicine, said the trial should go ahead. “Absolutely yes,” he said when asked whether it was ethical to offer a regimen that may provide only partial protection.Frontline workers already face substantial risks, existing evidence suggests the vaccines may offer some broader protection, and the observational study would involve only a limited number of volunteers, leaving opportunities to test Bundibugyo-specific vaccines later, Caplan said.The proposal could also help answer an important scientific question.Existing Ebola vaccines generate immune responses that recognize Bundibugyo, but it’s unknown whether those responses are strong enough to protect people from disease.“We don’t know whether that level of antibodies would be beneficial or meaningless,” Mark Feinberg, chief executive officer of the International AIDS Vaccine Initiative that’s developing vaccines against both the Sudan and Bundibugyo Ebola viruses, said in an interview. “We just don’t know.”Research on macaques at the University of Texas Medical Branch in Galveston found that monkeys given sequential vaccines against the Sudan and Zaire Ebola viruses several weeks apart survived after being deliberately exposed to the Bundibugyo virus, while most animals receiving the two vaccines simultaneously did not. The findings suggested a so-called prime-boost strategy might broaden protection, though not necessarily prevent illness altogether.Studying people who have already received Ervebo or IAVI’s Sudan Ebola vaccine in countries such as Rwanda or Uganda could help researchers better understand the immune responses generated by different vaccination strategies, Feinberg said.WHO GuidanceA scientifically robust and ethically conducted study of Ervebo, with or without a Sudan Ebola vaccine, would be consistent with World Health Organization recommendations, provided it meets established scientific, ethical and regulatory standards, said Vasee Moorthy, who leads the agency’s research and development work on emerging epidemic threats.WHO continues to advise against using Ervebo more broadly against Bundibugyo outside controlled research settings because evidence of cross-protection remains limited. Broader deployment may fail to confer protection against the disease and “could generate a false sense of security among affected communities and responders, potentially undermining trust and adherence to proven public health measures and damaging confidence in Ebola vaccination if breakthrough infections occur,” he said in an email.The possibility that breakthrough infections could undermine confidence in Ebola vaccination is “not unimportant,” said Armand Sprecher, an emergency physician and epidemiologist with Médecins Sans Frontières, in an interview from the Congolese city of Bunia, where 35 health workers have been infected, 14 fatally. The decision to receive a vaccination regimen thought to provide only partial protection should ultimately rest with healthcare workers after informed consent, he said.“Something is better than nothing and we know that it’s safe. It is your choice,” Sprecher said, adding that healthcare workers are capable of understanding that trade-off after informed consent.Africa CDC plans to seek rapid ethical approval because Ervebo is already licensed and IAVI’s experimental Sudan Ebola vaccine was used during Uganda’s 2025 Sudan Ebola outbreak. The agency is also discussing contributing an initial $500,000 to launch the study while seeking additional funding from partners.“An initial study could provide safety and immune-response data,” Africa CDC said. “Further studies would be required to establish whether the approach prevents infection, severe disease, or death.”More stories like this are available on bloomberg.comPublished on July 21, 2026