Africa CDC to deploy Zaire vaccine against faster-spreading Bundibugyo Ebola strain

The head of Africa's disease control agency stood before reporters on Thursday with a calculated gamble: use a vaccine designed for one Ebola strain to fight a different one that is spreading with terrifying speed. Jean Kaseya, director general of the Africa Centres for Disease Control, announced that authorities would begin deploying the existing Zaire strain vaccine against the current Bundibugyo outbreak ravaging eastern Democratic Republic of Congo. The decision rests on early evidence that, while vaccinated people still developed symptoms, none of them died.

The numbers driving this choice are stark. Since the outbreak was declared in mid-May, roughly 4,000 cases have been confirmed across 51 health zones—a geographic spread that has accelerated far beyond what epidemiologists expected. The Bundibugyo strain is moving through the population six to eight times faster than any Ebola outbreak on record. For context, the massive West African epidemic of 2014 to 2016, the largest in history, killed people at a slower rate than what is happening now in the DRC. The current outbreak is already the second-largest ever recorded, and it has been active for only a few months.

What makes this outbreak particularly alarming is not just its speed but the efficiency with which it finds new victims. During the previous Zaire strain outbreak in the DRC from 2018 to 2020, health workers identified one confirmed case for every 57 contacts they traced. In Uganda's smaller outbreak this year, that ratio was one case per 41 contacts. In the current DRC outbreak, the ratio has collapsed to one confirmed case for every ten people on the contact list. Kaseya stated plainly that at this point, anyone in Bunia, the hardest-hit city, or anywhere in the Ituri region should be considered a potential contact—a way of saying the virus has become nearly impossible to contain through traditional tracking methods.

The vaccine strategy emerged from conversations between Kaseya and World Health Organization Director-General Tedros Adhanom Ghebreyesus. Both men acknowledged that the unprecedented severity of this outbreak demands investigation. They plan to launch studies to determine whether the virus has mutated or whether some other factor is driving its unusual aggression. Kaseya emphasized the point with deliberate understatement: "This outbreak is just expanding."

The practical challenge of actually deploying the vaccine in eastern DRC is substantial. The region is remote, marked by active armed conflict and insurgencies that complicate any health intervention. Initial vaccine rollouts will be limited trials, according to Placide Mbala, a professor at the Africa CDC. Authorities also plan to expand use of remdesivir, an antiviral drug that showed promise in Uganda, where only two of twenty patients died after treatment. But the logistics of moving vaccines and medications into a conflict zone remain unclear.

Meanwhile, the human toll continues to mount. As of Tuesday, 1,801 deaths had been confirmed. The response itself is fracturing under strain. Medical staff in the hardest-hit regions have launched strikes and protests, demanding payment or better working conditions—a crisis within the crisis that threatens to further weaken the outbreak response.

A secondary concern emerged near Kinshasa when a river barge carrying more than 300 passengers was intercepted after a passenger died with Ebola-like symptoms. Health teams deployed a mobile laboratory to the vessel in Maluku, northeast of the capital, to conduct screening. The capital has so far remained untouched by the outbreak, and authorities moved quickly to prevent that from changing. Kaseya clarified that the boat had originated in Mongala province, where no cases have been reported, though earlier reports had incorrectly identified it as coming from Kisangani, an affected area. Regardless of the origin, all passengers were screened as a precaution, with results still pending.

The decision to use a cross-strain vaccine represents a calculated risk born of desperation and limited options. Bundibugyo has historically been rare, leaving doctors with minimal experience treating it and no established vaccines or treatments. The Zaire vaccine offers something: evidence of protection against death, even if it cannot prevent infection. In an outbreak moving this fast, in a region this fractured, that may be the only tool available.