‘Not over the finish line’: Ebola vaccine development remains important
The next generation of Ebola vaccines may be able to address deficiencies seen in the first generation, researchers said, highlighting the importance of continuing to evaluate new candidates even as the world nears the approval of the first licensed vaccine against the disease.
“I don’t think we can be complacent about vaccine development for Ebola,” Daniel Bausch, MD, MPH&TM, director of the U.K. Public Health Rapid Support Team, told Infectious Disease News. “We’re not yet over the finish line.”
A dozen candidates
WHO’s vaccine pipeline tracker shows around a dozen Ebola vaccine candidates in various stages of development. One candidate, an Ebola virus glycoprotein (EBOV GP) nanoparticle vaccine developed by Novavax, has completed a randomized, blinded, dose-ranging phase 1 trial that examined safety and immunogenicity and evaluated a range of doses and dosing regimens.
During the trial, 230 healthy adults were recruited to evaluate four EBOV-GP antigen doses as single- or two-dose regimens with or without an adjuvant called Matrix-M (Novavax).
According to results published in The Journal of Infectious Diseases, all formulations were well tolerated, and the two-dose regimen with adjuvant produced a rapid increase in anti-Ebola virus GP immunoglobulin G titers in participants. Additionally, serum Ebola virus-neutralizing and -binding antibodies using wild-type Zaire ebolavirus or pseudovirion assays were three- to ninefold higher among recipients of two-dose EBOV GP with adjuvant, compared with placebo — responses that persisted through 1 year, according to the study.
“Novavax’s Ebola virus GP nanoparticle vaccine leverages our recombinant nanoparticle technology together with our novel adjuvant,” Louis F. Fries III, MD, senior vice president and chief medical officer at Novavax. told Infectious Disease News. “The vaccine is safe, stable at room temperature, demonstrates stability beyond 1 year and has shown protection at all dose levels against lethal Ebola virus in nonhuman primates. It is well-tolerated in humans and elicits strong antibody responses at low doses.”
The vaccine was developed to protect against the Zaire species of Ebola, which caused the West African epidemic and the ongoing outbreak in the Democratic Republic of the Congo (DRC) and has a case count nearly 100 times higher than other strains. But Fries said the company also has the capability to produce antigens for Sudan ebolavirus and Marburg virus.
“We believe there is a role for innovative, next-generation vaccines, such as this one, which addresses some of the deficiencies seen in the first generation of vaccines,” Fries said. “While we applaud support of the first generation of vaccines, we believe there are significant limitations to the current strategies and that our Ebola virus GP nanoparticle vaccine could provide a meaningful benefit against this serious public health threat.”
According to Fries, Novavax is waiting on third-party financial support to conduct further trials but said the company is “eager to move forward” because the vaccine “demonstrates significant advantages over the live-vectored vaccine candidates currently being supported.”
Merck vaccine nears approval
Merck’s V920 vaccine, which protects against the Zaire species, has been widely used in the DRC outbreak and has been shown to be 97% effective. An FDA decision on U.S. approval is expected by the spring, and the European Medicines Agency has already recommended granting the vaccine conditional marketing authorization in the European Union. Another vaccine, this one manufactured by Johnson & Johnson, was scheduled to be introduced to the DRC this month.
Bausch, who wrote an accompanying comment on the study by Fries and colleagues, explained the virtue of continuing to research new Ebola vaccines in the presence of candidates that already appear to be effective.
“Each candidate vaccine comes with distinct features with regard to cold chain requirement, coverage of different species of Ebola virus, anticipated adverse effects and duration of immunity, and ease of manufacturing and administration,” he said. “A robust single-dose vaccine conferring long-term protection against all species of Ebola virus is the goal, and none of the leading candidates would provide this. I think we still should be exploring multiple candidates and platforms.”
Bausch said, on occasion, even the most promising vaccine candidates can be found to have rare but important adverse effects, sometimes even after regulatory approval and commercial availability. – by Caitlyn Stulpin
Bausch DG, et al. J Infect Dis. 2019;doi:10.1093/infdis/jiz520.
WHO. Vaccine pipeline tracker: Ebola & Marburg viruses. https://docs.google.com/spreadsheets/d/19otvINcayJURCMg76xWO4KvuyedYbMZDcXqbyJGdcZM/pubhtml#. Accessed October 28, 2019.
Disclosures: Bausch and Fries report no relevant financial disclosures.