Why is a Rare Ebola Strain Spreading So Fast, and What Are Scientists Doing to Stop It?

The Democratic Republic of the Congo is currently facing the second-largest and fastest-growing Ebola outbreak on record, caused by the rare Bundibugyo strain. Since the outbreak was declared on May 15, the virus has infected 3,802 people and claimed 1,707 lives. With no approved vaccines or targeted treatments available for this specific variant, health organizations are rushing experimental candidates into human trials at an unprecedented pace.

What Is Happening

Health officials are battling a rapidly expanding Ebola epidemic concentrated heavily in the eastern province of Ituri, which accounts for nearly 90 percent of all reported cases. The virus has killed more than 1,700 people out of 3,802 recorded cases, according to government figures. Over 17,000 contacts are currently being monitored by health teams, with roughly 80 percent followed up daily.

Unlike previous major outbreaks driven by the Zaire strain, this epidemic is caused by the Bundibugyo ebolavirus. Because there are no licensed vaccines or therapeutics for this specific strain, medical authorities are attempting to contain the spread using standard infection control measures while racing to test experimental interventions.

The Background

The current outbreak is spreading faster than any previously recorded Ebola epidemic. During the massive 2014–2016 West Africa outbreak, which ultimately infected about 28,000 people and killed over 11,000, it took roughly eight months for the death toll to reach 1,000. In this crisis, the death toll breached 1,700 in less than three months.

The World Health Organization declared the outbreak a Public Health Emergency of International Concern on May 17. Neighboring Uganda previously declared itself Ebola-free in mid-June after discharging its last patient, but the region remains at high risk of re-introduction as infections spread across five other provinces in the DRC, including the major city of Kisangani.

Bundibugyo ebolavirus

A rare species of the filovirus family causing severe hemorrhagic fever, for which no approved vaccine or treatment currently exists.

Post-exposure prophylaxis

A preventative medical treatment administered after potential exposure to a pathogen to prevent the onset of infection.

The Latest Development

In response to the escalating crisis, international regulators and research bodies have authorized rapid Phase 1 clinical trials for experimental vaccines. Health Canada authorized Moderna to launch human trials for its mRNA-1469 vaccine candidate, with the first volunteer receiving a dose on August 3 in Truro, Nova Scotia. Additional trial sites are active in Halifax and Toronto, aiming to enroll approximately 80 healthy adult volunteers.

The trial is supported by up to $50 million from the Coalition for Epidemic Preparedness Innovations (CEPI). Another vaccine trial, developed by the University of Oxford using a viral-vector platform, began human testing in the United Kingdom on July 24. A clinical trial evaluating an oral post-exposure prophylaxis medicine given over 10 days to high-risk contacts is also underway in Ituri province, with over 25 patients enrolled.

Getting Moderna's vaccine candidate into a Phase 1 trial this rapidly is a major step forward in the fight against this deadly outbreak.

What It Means

For the communities affected in central Africa, the rapid development of experimental vaccines offers a potential line of defense, though practical relief remains months away. Phase 1 trials only measure safety, dosage, and basic immune response; larger Phase 2 and Phase 3 trials will still be required to prove efficacy before regulatory bodies can approve wider distribution.

If licensed, Moderna has committed to supplying at least 500,000 doses to low- and middle-income countries under access pricing through its agreement with CEPI. However, infectious disease experts warn that clinical trials could take over a year to complete, meaning immediate containment must rely on field intervention, contact tracing, and early isolation.

What Remains Unclear

Several critical factors regarding the outbreak and response remain unresolved:

• Peak Timing: Health officials, including Africa CDC Director-General Jean Kaseya, acknowledge it remains unclear when the outbreak will peak.
• Vaccine Efficacy: Preclinical animal data is promising, but only human clinical trials will establish whether any of the four CEPI-backed vaccine candidates provide real-world protection against the Bundibugyo strain.
• Cross-Protection Potential: Scientists are still evaluating whether existing vaccines for the Zaire strain, such as Ervebo, offer any partial cross-protection against Bundibugyo.
• Operational Security and Funding: Over 100 healthcare workers have been infected, and frontline teams face severe wage delays, ongoing violence from armed groups, local mistrust, and critical aid funding shortfalls.

Frequently Asked Questions

What strain of Ebola is causing the current outbreak?

The outbreak is caused by the Bundibugyo species of the Ebola virus, a rare variant for which no licensed vaccines or treatments currently exist.

How many cases and deaths have been reported?

As of early August, official figures record 3,802 cases and 1,707 deaths, making it the second-largest Ebola outbreak in history.

Where are the new vaccine trials being conducted?

Phase 1 trials for Bundibugyo vaccine candidates are actively underway in Canada (Toronto, Halifax, and Truro) and the United Kingdom.

How does the Bundibugyo strain compare to previous outbreaks?

This epidemic is spreading faster than the 2014–2016 West Africa outbreak, reaching over 1,700 deaths in under three months compared to eight months in the 2014 crisis.

When will an Ebola vaccine for this strain be publicly available?

Definite conclusions and safety data from early trials will take several months, and full Phase 2 and 3 efficacy trials are required before any candidate receives regulatory approval.