WHO hopes to test an experimental Marburg virus vaccine amid an outbreak in Equatorial Guinea

The World Health Organization hopes to test an experimental Marburg vaccine in Equatorial Guinea, which announced its first outbreak of the virus Monday.

Nine deaths have been confirmed, while 16 suspected patients are in quarantine. Health officials are also monitoring 15 asymptomatic close contacts of infected people.

No vaccine or antiviral treatment is approved to treat Marburg virus disease, which has an average death rate of around 50%, according to the WHO.

On Tuesday, the WHO convened an urgent meeting to evaluate several possible vaccine candidates that could be administered during the outbreak. The meeting brought together a consortium of vaccine developers, researchers and government officials — a group the WHO created in 2021 to advance a Marburg vaccine.

“Everything that we do needs to be done with alacrity," Dr. Philip Krause, the chair of the WHO Covid Vaccines Research Expert Group, said at the meeting. "Even if we’re going to do a study over many outbreaks, the more participants in that study that could be enrolled at each outbreak, the more likely we are to reach a conclusion sooner."

People can spread Marburg virus through blood, other bodily fluids or contaminated objects or surfaces. Past outbreaks, mostly in Africa, have had death rates of 24% to 88%, depending on the virus strain and the strength of efforts to control transmission.

Marburg belongs to the same family of viruses as Ebola, so the diseases can look similar. Both are characterized by viral hemorrhagic fever, a condition that can cause internal bleeding and damage multiple organ systems.

Marburg virus disease usually starts with fever, chills, headache or muscle aches, followed by a rash and nausea, vomiting, diarrhea, sore throat or chest or stomach pain, according to the Centers for Disease Control and Prevention. Ebola follows a similar progression from "dry" to "wet" symptoms.

George Ameh, the WHO’s representative in Equatorial Guinea, said the organization has ramped up contact tracing. The outbreak's first case most likely dates to Jan. 7, he said, but the country’s health ministry learned about it a month later. Deaths have been among close family members and people who attended their burials, he added.

Before this, the most recent Marburg outbreak was in Ghana in July. It resulted in three cases, two of which were fatal. Before that, Guinea reported one death in 2021, but the virus did not spread to any of the person’s contacts.

The Marburg virus, which originates in fruit bats, was first detected in 1967 among people who had been exposed to African green monkeys.

Attendees at the WHO meeting discussed five vaccine candidates that have shown promise against Marburg virus in animal studies. Three vaccine developers — Janssen Pharmaceuticals, Public Health Vaccines and the Sabin Vaccine Institute — said they could probably make doses available to test in the current outbreak.

The vaccines from Janssen and Sabin have already gone through phase 1 clinical trials. Public Health Vaccines' shot was recently found to protect against the virus in monkeys, and the Food and Drug Administration has cleared it for human testing.

The WHO said its next step is to convene a group of independent experts to pick which vaccine candidate to prioritize. The organization said it will work with clinicians and health officials in Equatorial Guinea to determine what a trial might look like.

But some at the meeting pointed out that there may not be enough cases in this outbreak to properly evaluate a vaccine.

"If you look at the past history of Marburg outbreaks, they're generally quite small, and the interventions that have been put in place have limited their size," said John Edmunds, an epidemiology professor at the London School of Hygiene and Tropical Medicine.

Nancy Sullivan, the chief of biodefense research at the U.S. government’s Vaccine Research Center, said the outbreak may be difficult to trace because of movement across the border. Equatorial Guinea has restricted movement between its affected districts and quarantined more than 200 people to prevent the virus from spreading.

“While the [health ministry] has done a great job of tracking cases, I think we would be foolish to assume that no cases have gone undetected," Sullivan said.