Two candidate Ebola vaccines developed as possible next-generation products fully protected monkeys immunized with a single dose against experimental infection with the strain responsible for West Africa's outbreak, researchers reported today.
The vaccines are intermediate and highly attenuated versions of a vesicular stomatitis virus (VSV) vaccine that contains the Ebola virus glycoprotein. A team from the University of Texas Medical Branch (UTMB) at Galveston and Profectus BioSciences, Inc., reported its findings today in the latest issue of Nature.
Human safety and efficacy trials are under way in Liberia and Guinea on the first-generation version of the vaccine, VSV-EBOV, which was developed by researchers at the Public Health Agency of Canada and licensed by NewLink Genetics and Merck. Recent phase 1 studies of VSV-EBOV showed that the vaccine quickly prompted a good immune response, but also triggered some expected self-limiting reactions such as fever, as well as arthritis and rash in a few participants, that are inherent in a live attenuated VSV vaccine.
The UTMB-Profectus research team said early indications suggest that a further-attenuated VSV vaccine, with fewer safety concerns, may be more desirable for widespread administration in parts of Africa where Ebola is endemic.
Like the other candidate Ebola vaccines, the two VesiculoVax-platform vaccines contain genetic material from the original 1976 Mayinga Ebola strain, which is 97% similar to the current outbreak strain.
Eight vaccinated and two unvaccinated control macaques were infected with the Makona strain of Ebola (formerly called the Guinea strain) 28 days after receiving a single dose of one of the vaccines. Both vaccines protected animals after a single dose. None developed severe signs of illness, and the two unvaccinated animals died 7 and 8 days after they were experimentally infected.
John Eldridge, PhD, chief scientific officer for Profectus, said in a company press release that the trial is the first to show rapid single-dose protection against the strain of Ebola Zaire responsible for the ongoing epidemic in West Africa. He added that the company is buoyed by the vaccine's potential to help battle the current outbreak and looks forward to advancing it and a trivalent vaccine against all Ebola and Marburg viruses into human clinical trials.
Both vaccines dropped the level of VSV in the blood tenfold compared with the first-generation vaccine, according to a UTMB press release.
Testing was done at the Galveston National Laboratory, a biosafety level 4 facility on the UTMB campus.
Apr 8 Nature abstract
Apr 8 UTMB press release
Apr 8 Profectus press release
Apr 1 CIDRAP News story "Phase 1 trials of Ebola vaccine show good immune responses"