The quest for an effective vaccine against Ebola has moved a step closer to reality, scientists say, after an experimental nasal spray was found to offer long-lasting protection against the deadly Ebola virus in animal studies.
In trials with non-human primates, a single inhaled dose of the experimental vaccine successfully prevented 100 percent of the animals from contracting the deadly virus, even a year after it was administered.
Results of the pre-clinical study — published this week in the journal Molecular Pharmaceutics — offer the only evidence to date that a non-injectable vaccine can effectively buffer against future Ebola infection.
Should it work in humans, the vaccine could have significant global implications in controlling future outbreaks, says co-principal investigator Dr. Maria A. Croyle, a professor in the College of Pharmacy at the University of Texas at Austin. She and her group worked on the vaccine with a team at the National Microbiology Laboratory in Winnipeg led by co-principal investigator Dr. Gary Kobinger.
According to the researchers, the vaccine delivery system could surmount the logistical obstacles of storing, transporting and administering injectable vaccines in parts of Africa most afflicted by the virus.
Nasal spray could meet ‘desperate need’ for vaccine
Ebola was first discovered in 1976 near the Ebola River in what is now the Democratic Republic of the Congo. Since then, outbreaks have appeared sporadically in Africa, killing between 25 percent to 70 percent of those infected, depending on the strain.
While scientists are making great progress toward understanding the biology of Ebola, there are not yet any licensed treatments or vaccines for the virus.
The current epidemic of Ebola in West Africa – where around 70 percent of cases are fatal – is the largest and most complex the world has ever seen. The World Health Organization (WHO) has declared the outbreak a public health emergency of international concern, citing it as the “greatest peacetime challenge” the UN agency has ever faced.
“There is a desperate need for a vaccine that not only prevents the continued transmission from person to person, but also aids in controlling future incidences,” said doctoral student Kristina Jonsson-Schmunk, who worked on the project alongside Dr. Croyle at UT-Austin.
Inhalable vaccine improved survival in non-human primates
Several Ebola vaccines have been in the works for years, but the pharmaceutical industry has not been motivated to invest in them because the prospective market was too small — before now, Ebola had only infected a few thousand people — and could not meet the profit-driven criteria of drug companies.
Dr. Croyle’s team has been working on the development of an inhalable form of an Ebola vaccine for over 7 years. The breathable vaccine targets cells in the nasal passages and in the lungs, and causes a body-wide immune system response. It affects the mucosa, thus preventing the virus from entering the eyes, nose and mouth, as well as through a cut in the skin. These are the main routes of entry of the virus into the body.
In this latest phase of development, the researchers carried out trials of the inhaler in non-human primates and found it increased survival of immunized animals from 67 percent to 100 percent when the animals were infected with 1,000 plaque-forming units of Ebola 150 days after immunization. The strain used was the Zaire strain – the one currently circulating in West Africa.
“The formulated vaccine was fully protective against challenge 21 weeks after immunization,” the authors report. In comparison, when the animals were given the vaccine by the standard method of intramuscular injection, only 50 percent survived the infection challenge.
Intranasal delivery system offers an edge over other vaccines
Dr. Croyle says the main advantage of their vaccine over others currently undergoing clinical testing is that it offers long-lasting protection after a single inhaled dose, while the longevity of other candidate vaccines has not yet been established. “Moreover, this immunization method is more attractive than an injectable vaccine given the costs associated with syringe distribution and needle safety and disposal,” she adds.
The vaccine’s needle-free delivery system is particularly important given that accidental needle injuries are one way health care workers are getting infected with Ebola, says Dr. Croyle. She also believes the vaccine may be stable at room temperature — a critical factor when delivering immunizations in hot areas without electricity.
The next stage of research for Dr. Croyle’s team is a phase I clinical trial that will test the effectiveness of their vaccine on 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 non-human primates.
Currently, there are six vaccines at different stages of development — three in the United States, one in Britain, one in Mali and one in Switzerland. In Mali, the vaccine being tested is also using a common cold virus, though it relies on a needle-based delivery system. If the vaccines are shown to be safe in preliminary trials, they will next be tested on healthcare workers fighting Ebola in West Africa.