Workings of Ebola vaccine decoded; smaller dose seen yielding similar protection

Israeli and German scientists have decoded how the body’s immune system reacts to a poorly understood vaccine against the deadly Ebola disease, and how the body generates effective antibodies against the disease.

The findings could have implications for how the medicine could provide a long-term defense against the epidemic.

Over 100,000 people have received Ebola vaccines so far, but the medicines are not well understood. Researchers don’t know how effective the vaccines will be at providing long-term immunity, how well they’ll work for large groups of people, or how exactly the medicines affect the immune system.

The fatality rate for Ebola is roughly 50 percent, and can be up to 90%, according to the World Health Organization.

In the 2013-2016 outbreak in West Africa, 11,325 people died and 28,600 were infected. Most people who survive the disease have immunity, although there are often lingering health effects, according to the Centers for Disease Control and Prevention.

Existing vaccines are unwieldy — they are hard to produce, and there aren’t enough available to vaccinate broad swaths of the population. It is also difficult to reach certain areas threatened by the disease due to civil unrest, Dr. Ron Diskin of the Weizmann Institute of Science said in a statement.

The medicines are therefore usually administered to the people most threatened with infection.

“Understanding exactly how the immune response is produced following vaccination will not only help refine the vaccine itself, it can help us understand whether it will work against different strains of the virus or whether the dose given today is the best one,” Diskin said.

A child is vaccinated against Ebola in Beni, DRC, July 13, 2019. (AP Photo/Jerome Delay, file)

Two groups of scientists, from Israel’s Weizmann Institute of Science and Germany’s University of Cologne, teamed up to better understand the virus. The results of their study were published in the peer-reviewed journal Nature Research on October 7.

Scientists at the University of Cologne started the study by searching for signs of an immune response in blood samples from six people who had previously received the vaccine, which is called rVSV-ZEBOV.

The team examined the subjects’ B cells, a type of white blood cell that produces antibodies that “remember” diseases. The researchers isolated individual antibodies from the B cells that had bound to virus proteins.

Then, Israeli researchers from the Weizmann Institute chose two antibodies to focus on, which they thought likely to be involved in the subjects’ long-term immune response.

They first worked to understand how and where the antibodies bind to the virus’s outer membrane as part of the vaccine immune response, and how the binding neutralized the virus.

The team found its answer with a high-powered electron microscope recently acquired by the Weizmann Institute in the first use of the device in any study. The microscope can display the three-dimensional structure of the antibody bound to the virus.

Burial workers wearing protective gear carry the remains of Mussa Kathembo, an Islamic scholar who had prayed over those who were sick and died of Ebola, in Beni, DRC, July 14, 2019. (AP Photo/Jerome Delay)

Using these images, researchers were able to show how the two antibodies the team had singled out were so efficient at combating the virus. Many antibodies from the B cells bound to the viruses, but the two the team looked at bound to sites on the virus’s membrane that were more vulnerable, and bound to them in a different way than the other antibodies.

They created a map showing where the antibodies bound to the viruses, and compared that map to the antibody binding sites of Ebola survivors, which provide effective protection. Survivors of the disease rarely get it again.

The two maps turned out to be nearly identical. The German research team then tested the antibodies against a live Ebola virus, proving its efficacy.

Subjects who had received a smaller dose of the vaccine had a similar number of antibodies to subjects who had received a higher dose, meaning that health officials might be able to afford to provide more people with the medicine.

Scientists still don’t know if the vaccine will be an effective defense against other Ebola strains, however.