Vaccinations for Sudan Ebola virus begin in Uganda to curb outbreak

On Jan. 30, Uganda confirmed an outbreak of the Sudan virus disease. The Sudan virus belongs to the same family as the Ebola virus. The announcement came after the death of a 32-year-old nurse in the capital, Kampala, who tested positive for the virus during a postmortem assessment. He initially developed high fever and chest pain and had difficulty breathing. Within days, the individual experienced bleeding and later died from multiorgan failure. Before visiting the hospital where he passed away, the nurse had sought treatment at multiple health facilities and from a traditional healer.

As of Feb. 4, Uganda identified 298 close contacts of the deceased person, including health-care workers who cared for him. Officials have confirmed six additional cases that are positive for the Sudan virus. They’re continuing to trace and test these contacts and quarantine individuals who are at high risk. Authorities don’t yet know how the nurse got infected, but investigations are ongoing, said Otim Patrick, an epidemiologist and senior health emergency officer at the World Health Organization (WHO) - Regional Office for Africa, during a Feb. 6 webinar.

Sudan virus disease occurs when humans come in contact with dead or sick animals infected with the virus. Scientists suspect fruit bats to be the primary hosts of the virus. They’ve also documented Sudan virus infections in nonhuman primates, including gorillas, chimpanzees, and monkeys. Among humans, the disease typically spreads via infected body fluids and by touching contaminated surfaces.

Scientists analyzed virus isolates from the ongoing outbreak and found no link to Uganda’s previous outbreak in 2022–23, which resulted in 164 cases of Sudan virus disease and 55 deaths. (The country has had six Sudan virus disease outbreaks since 2000.) Instead, in the WHO update webinar, Patrick mentioned that the currently circulating virus strain is similar to the one involved in the 2012 outbreak, indicating that an independent animal-to-human spillover may have occurred in the same ecological region.

There are no approved vaccines or treatments for Sudan virus disease, which has a 40–70% fatality rate. To curb the ongoing outbreak, Uganda has deployed—under a clinical trial setting—a vaccine candidate developed by the International AIDS Vaccine Initiative (IAVI).

The recombinant vesicular stomatitis virus vaccine is altered to express the Sudan virus glycoprotein, “which essentially is the key that lets these viruses access our cells and cause infection,” says Logan Banadyga, a molecular virologist specializing in the study of filoviruses, including Ebola, at Canada’s National Microbiology Laboratory. The vaccine triggers an immune response to the Sudan virus glycoprotein that generates antibodies that could help protect people from getting sick if exposed to the virus.

IAVI researchers and their colleagues tested the vaccine in macaques and found that a single dose protected up to 100% of the animals for at least 28 days following vaccination. Meanwhile, all unvaccinated macaques infected with the Sudan virus died by day 9. The team also found the vaccine to be safe and immunogenic in a Phase I trial they conducted in humans. The researchers presented these findings in Nov. 2024 at the American Society for Tropical Medicine and Hygiene Annual Meeting. In Uganda, however, scientists at the Makerere University and the Uganda Virus Research Institute are testing the efficacy of this vaccine candidate.

The trial—launched just 4 days after the declaration of the outbreak—is the first to evaluate the clinical efficacy of a vaccine against the Sudan virus. “It’s actually quite remarkable,” Banadyga says. “We’re getting vaccines into arms in record time.”

In next steps, as part of the Solidarity trial the WHO launched during the 2022 Sudan virus disease outbreak, Uganda will resume testing a two-antibody pan-Ebolavirus cocktail drug called MBP134 to treat Sudan virus disease. Until then, patients are receiving antiviral remdesivir to help protect against severe disease.