At Last: Ebola Vaccine Deemed a Success

by Lynn Hetzler via Multibriefs

Ebola is one of the deadliest viruses known to medical science. In just one outbreak occurring between December 2013 and April 2016, there were 28,600 cases of Ebola and 11,300 deaths in Guinea, Liberia and Sierra Leone. That outbreak — the largest Ebola virus disease outbreak in history — sparked an international hunt for an effective vaccine.

A team of researchers at St George's, University of London, now reports that one Ebola vaccine produces an immune response to the virus, and that the vaccine is safe for use in adults and children.

Ebola virus disease (EVD) has an average mortality rate of around 50 percent, according to the World Health Organization (WHO). Case fatality rates can be as high as 90 percent.

Results from a trial in Guinea shows using 2 x 107 plaque-forming units (PFU) of rVSVΔG-ZEBOV-GP vaccine prevented EVD. This study provides additional safety and immunogenicity data about the rVSVΔG-ZEBOV-GP vaccine.

The St George's researchers worked with colleagues on a vaccine trial in Gabon, a country along the Atlantic coast of Central Africa. In 2001, there were 65 cases of Ebola virus disease in Gabon and 53 deaths. While this outbreak caused significant illness and mortality, it failed to spur scientific investigation into EVD vaccines. After the largest outbreak in history ended in 2016, researchers from around the world set up trials in hopes of developing a vaccine that could prevent future EVD outbreaks.

Testing in a country that has experienced EVD outbreaks in the past, such as Gabon, shows vaccination can even boost immunity for those exposed to the Ebola virus and have consequently developed antibodies to Ebolavirus glycoprotein.

"An unprecedented Ebola outbreak showed how it is possible for academics, nongovernmental organizations, industry and funders to work effectively together very quickly in times of medical crisis," co-author of the study Sanjeev Krishna said. "The results of the trial show how a vaccine could best be used to tackle this terrible disease effectively."

Krishna went on to say a system of specialists, medical experts and organizers are necessary to remain vigilant against outbreak diseases like EVD.

"We should continue to improve ways to make, evaluate and deliver vaccines when they are needed, often in parts of the world lacking in infrastructure for diagnosing infections and providing treatments," he said.

rVSVΔG-ZEBOV-GP contains a noninfectious portion of a Zaire Ebola virus gene. The vaccine was one of WHO's two "candidate" options for combating Ebola virus outbreaks in West Africa.

A team of researchers from University of Tübingen in Germany led the clinical trial to establish the safety and immunogenicity of rVSVΔG-ZEBOV-GP. Professor Peter Kremsner coordinated the effort with their partner institute CERMEL in Lambaréné, Gabon.

The primary objective of the trial was to determine safety and tolerability of the vaccine 28 days after injection. Secondary objectives included immunogenicity, viremia and shedding post-vaccination.

The researchers enrolled 115 adults, 20 adolescents and 20 children into a randomized, open-label phase I trial in Lambaréné, Gabon. The team administered five single intramuscular vaccine doses of 3 x 103, 3 x 104, 3 x 105, 3 x 106, or 2 x 107 PFU to adults. Children and adolescents received doses of 2 x 107 PFU.

Prior to vaccination, the research team detected Zaire Ebola virus (ZEBOV)-glycoprotein (GP)-specific and ZEBOV antibodies in 11 and 27 percent of adults, respectively. At day 28, 74 to 100 percent of adults who received a dose 3 x 104, 3 x 105, 3 x 106, or 2 x 107 PFU had a ≥4.0-fold increase in geometric mean titers (GMTs) of ZEBOV-GP-specific antibodies, reaching GMTs of 489, 556, 1,245, and 1,503, respectively.

The researchers detected neutralizing antibodies in more than half of participants at doses ≥3 x 105 PFU. Antibodies were present up to day 180 for doses ≥3 x 105 PFU; adults with antibodies prior to vaccination had higher GMTs throughout the study period.

Adults experienced frequent mild to moderate adverse events related to vaccination, but neither adults, adolescents nor children reported any serious or adverse events. Krishna also notes that further research into lower doses for children and adolescents is necessary for continual replication of the vaccine.

Lynn Hetzler has been a freelance writer for more than 15 years. She has extensive experience in a variety of specialties, including transplantation, oncology, fertility, negligible senescence, laboratory science, addiction, general research and more. Lynn specializes in creating informative and engaging medical content for readers of all levels, from patients to researchers and everyone in between.