A single dose of a breathable Ebola vaccine has been shown to provide long-lasting protection to nonhuman primates. The vaccine, a respiratory formulation based on an adenovirus, improved survival of immunized nonhuman primates from 67 to 100% after the challenge with 1,000 plaque-forming units of Ebola Zaire—the strain currently ravaging West Africa. Protection was recorded to last as long as 150 days after immunization.
These results emerged from a preclinical study that was led by Maria Croyle, Ph.D., an associate professor of pharmaceutics at the University of Texas at Austin’s College of Pharmacy, and Gary Kobinger, Ph.D., head of vector design and immunotherapy at the National Microbiology Laboratory in Winnipeg. The researchers summarized their findings November 1 in the journal Molecular Pharmaceutics, in an article entitled, “A Single Dose Respiratory Recombinant Adenovirus-Based Vaccine Provides Long-Term Protection for Non-Human Primates from Lethal Ebola Infection.”
“Diverse populations of polyfunctional Ebola GP-specific CD4+ and CD8+ T cells and significant anti-Ebola GP antibodies were present in samples collected 150 days after respiratory immunization,” wrote the authors. “The formulated vaccine was fully protective against challenge 21 weeks after immunization.”
The results cited above refer to just one part of the study. In another part, one in which the vaccine was administered by intramuscular injection, just 50% of the primates survived challenge.
“The main advantage of our vaccine platform over the others in clinical testing is the long-lasting protection after a single inhaled dose,” noted Dr. Croyle. “This is important since the longevity of other vaccines for Ebola that are currently being evaluated is not fully evaluated. Moreover, this immunization method is more attractive than an injectable vaccine given the costs associated with syringe distribution and needle safety and disposal.”
Besides the logistical and cost issues that would attend the storage, transport, and administration of injectable vaccines in parts of Africa most afflicted by the virus, there are also, as Dr. Croyle indicated, issues of safety. When healthcare workers must make use of needles, they are at risk of accidental needle injury, particularly when they are encumbered by elaborate protective garb. Such injury is one way healthcare workers may acquire Ebola from patients.
The researchers look forward to attempting clinical trials that could assess the effectiveness of their vaccine in human subjects. They will also further explore preliminary data they have collected for administration of the vaccine as a thin film under the tongue in nonhuman primates. These issues, and others, may be discussed when Dr. Croyle delivers a presentation about the new vaccine November 5 at the 2014 annual meeting of the American Association of Pharmaceutical Scientists.