Ebola vaccine
Ebola vaccine candidates against Ebola have been developed in the decade prior to 2014,
but none have yet been approved for clinical use in humans. Several promising vaccine candidates have been shown to protect nonhuman primates (usually macaques) against lethal infection. These include replication-deficient adenovirus vectors, replication-competent vesicular stomatitis (VSV) and human parainfluenza (HPIV-3) vectors, and virus-like nanoparticle
preparations. Conventional trials to study efficacy by exposure of
humans to the pathogen after immunization are obviously not feasible in
this case. For such situations, the FDA has established the "Animal Efficacy Rule" allowing licensure to be approved on the basis of animal model studies that replicate human disease, combined with evidence of safety and a potentially potent immune response (antibodies in the blood) from humans given the vaccine. Clinical trials
involve the administration of the vaccine to healthy human subjects to
evaluate the immune response, identify any side effects and determine
the appropriate dosage.
| Vaccine | Associated organisations |
Status |
|---|
| Chimp adenovirus 3 vectored glycoprotein (cAd3-EBO Z) |
GSK & NIAID |
Phase III Feb. 2016 |
| rVSV vectored glycoprotein (VSV-EBOV) |
Newlink Genetics & Merck |
in use (flare ups/ West Africa) |
| Human adenovirus 5 vectored 2014 glycoprotein insert |
BIT & CanSino |
Phase I complete |
| Adenovirus 26 vectored glycoprotein / MVA-BN (Ad26.ZEBOV/ MVA-BN) |
Johnson & Johnson |
Phase I complete April, 2016 |
| HPIV-3 vectored glycoprotein |
Ministry of Health (Russia) |
Phase I planned |
| Rabies vectored glycoprotein |
Thomas Jefferson University & NIAID |
Non-human primate challenge complete |
| Purified glycoprotein |
Protein Sciences |
NHP challenge initiated |
| Ebola ∆VP30 H2O2 treated |
University of Wisconsin |
Non-human primate challenge complete |
In September 2014, two Phase 1 clinical trials began for the vaccine cAd3-EBO Z, which is based on an attenuated version of a chimpanzee adenovirus (cAd3) that has been genetically altered so that it is unable to replicate in humans.
The cAd3 vector has a DNA fragment insert that encodes the Ebola virus
glycoprotein, which is expressed on the virion surface and is critical
for attachment to host cells and catalysis of membrane fusion. It was developed by NIAID in collaboration with Okairos, now a division of GlaxoSmithKline.
For the trial designated VRC 20, 20 volunteers were recruited by the
NIAID in Bethesda, Maryland, while three dose-specific groups of 20
volunteers each were recruited for trial EBL01 by University of Oxford,
U.K. Initial results were released in November 2014; all 20 volunteers
developed antibodies against Ebola and there were no significant
concerns raised about safety.
In December 2014, University of Oxford expanded the trial to include a booster vaccine based on MVA-BN, a strain of Modified vaccinia Ankara, developed by Bavarian Nordic, to investigate whether it can help increase immune responses further.
The trial which has enrolled a total of 60 volunteers will see 30
volunteers vaccinated with the booster vaccine. As of April 2015, Phase 3
trial with a single dose of cAd3-EBO Z begins in Sierra Leone after a
successful Phase 2 study in West Africa countries.
rVSV-EBOV
A vaccine based on the vesicular stomatitis virus which was genetically modified to express a surface glycoprotein of Zaire Ebola virus, called VSV-EBOV, has been developed by the Public Health Agency of Canada, with development subsequently taken over by Merck Inc. In October 2014, the Wellcome Trust, who was also one of the biggest UK founder, announced the start of multiple trials in healthy volunteers in Europe, Gabon, Kenya, and the USA.
The vaccine was proven safe at multiple sites in North America, Europe,
and Africa,but several volunteers at one trial site in Geneva,
Switzerland, developed vaccine-related arthritis after about 2 weeks,
and about 20%-30% of volunteers at reporting sites developed low-grade
post-vaccine fever, which resolved within a day or two. Other common
side-effects were pain at the site of injection, myalgia, and fatigue. The trial was temporarily halted in December 2014 due to possible adverse effects, but subsequently resumed.
As of April 2015, a Phase 3 trial with a single dose of VSV-EBOV began
in Liberia after a successful Phase 2 study in the West Africa country.
On 31 July 2015, preliminary results of a Phase 3 trial in Guinea
indicated that the vaccine appears to be "highly efficacious and safe." The trial used a ring vaccination
protocol that first vaccinated all the closest contacts of new cases of
Ebola infection either immediately or after 21 days. Because of the
demonstrated efficacy of immediate vaccination, all recipients will now
be immunized immediately. Ring vaccination is the method used in the program to eradicate smallpox in the 1970s. The trial will continue to assess whether the vaccine is effective in creating herd immunity to Ebola virus infection.
Ad26.ZEBOV/ MVA-BN
Johnson & Johnson has developed an Ebola vaccine at its Janssen Pharmaceutica Company. The regimen consists of two vaccine components (first vaccine as prime, followed by a second vaccine as boost) that are based on AdVac technology from Crucell Holland B.V., which is part of Janssen, and the MVA-BN technology from Bavarian Nordic.
The Ad26.ZEBOV is derived from human adenovirus serotype 26 (Ad26)
expressing the Ebola virus Mayinga variant glycoprotein while the second
component MVA-BN is the Modified Vaccinia Virus Ankara - Bavarian Nordic (MVA-BN) Filo-vector. This product commenced Phase 1 clinical trial at the Jenner Institute in Oxford during January 2015.
The preliminary data indicated the prime-boost vaccine regimen elicited
temporary immunologic response in the volunteers as expected from
vaccination. The Phase 2 trial enrolled 612 adult volunteers and
commenced in July 2015 in United Kingdom and France. A second Phase 2
trial, involving 1,200 volunteers, has been initiated in Africa with the first trial commenced in Sierra Leone in October 2015.
Ebola GP vaccine
Recombinant formation plasmids
At the 8th Vaccine and ISV Conference in Philadelphia on 27−28 October 2014, Novavax Inc. reported the development in a "few weeks" of a glycoprotein (GP) nanoparticle Ebola virus (EBOV GP) vaccine using their proprietary recombinant technology. A recombinant protein is a protein whose code is carried by recombinant DNA. The vaccine is based on the newly published genetic sequence of the 2014 Guinea Ebola
(Makona) strain that is responsible for the current Ebola disease
epidemic in West Africa. In animal studies, a useful immune response was
induced, and was found to be enhanced ten to a hundred-fold by the
company's "Matrix-M" immunologic adjuvant.
A study of the response of non-human primate to the vaccine had been
initiated. As of February 2015, Novavax had completed 2 primate studies
on baboons and macaques and had initiated a Phase 1 clinical trial in
Australia. The Lipid nanoparticle (LNP)-encapsulated siRNAs rapidly adapted to target the Makona outbreak strain of EBOV are able to protect 100% of rhesus monkeys against lethal challenge when treatment was initiated at 3 days postexposure while animals were viremic and clinically ill. The top line Phase 1 human trial results showed that the adjuvanted Ebola GP Vaccine was highly immunogenic at all dose levels.
Nasal vaccine
On November 5, 2014, the
Houston Chronicle reported that a research team at the University of Texas-Austin was developing a nasal spray Ebola vaccine, which the team had been working on for seven years.
The team reported in 2014 that in the nonhuman primate studies it
conducted, the vaccine had more efficacy when delivered via nasal spray
than by injection.
As of early November 2014 further development by the team appeared unlikely due to lack of funding.
Vaxart tablet
Vaxart
Inc. is developing a vaccine technology in the form of a
temperature-stable tablet which may offer advantages such as reduced cold chain
requirement, and rapid and scalable manufacturing. In January 2015,
Vaxart announced that it had secured funding to develop its Ebola
vaccine to Phase 1 trial.
Novel recombinant adenovirus type-5 vector-based Ebola vaccine
In late 2014 and early 2015, a double-blind, randomized Phase 1 trial was conducted in the Jiangsu Province of China; the trial examined a vaccine that contains glycoproteins
of the 2014 strain, rather than those of the 1976 strain. The trial
found signals of efficacy and raised no significant safety concerns.
Vesicular Stomatitis Virus vaccine
A study published in
Science
during March 2015 demonstrates that vaccination with a weakened form of
the Ebola virus provides some measure of protection to non-human
primates. This study was conducted in accordance with a protocol
approved by an Institutional Animal Care and Use Committee of the
National Institutes of Health. The new vaccine relies on a strain of Ebola called EBOVΔVP30, which is unable to replicate.
Clinical trials in West Africa
In January 2015, Marie-Paule Kieny, the WHO's
assistant director-general of health systems and innovation, announced
that the vaccines cAd3-EBO Z and VSV-EBOV had demonstrated acceptable
safety profiles during early testing and would soon progress to
large-scale trials in Liberia, Sierra Leone and Guinea. The trials would
involve up to 27,000 people and comprise 3 groups - members of the
first two groups would receive the two candidate vaccines, while the
third group will receive a placebo.
Both vaccines have since successfully completed the Phase 2 studies. The large scale Phase 3 studies have begun as of April 2015 in Liberia and Sierra Leone,
and in Guinea in March 2016
.
In addition, a medical anthropologist at Université de Montréal,
has been working in Guinea and raised further questions about safety in
the ring trial after spending time in April at one of the Ebola
treatment units where trial participants are taken if they become ill,
the centre in Coyah, about 50 km from the capital of Conakry.
U.S. national stockpile
Credit Suisse
has estimated that the U.S. government will eventually provide over $1
billion in contracts to companies to develop medicine and vaccines for
Ebola virus disease. Congress passed a law in 2004 that funds a national
stockpile of vaccines and medicine for possible outbreaks of disease. A
number of companies are developing Ebola vaccines: GlaxoSmithKline, NewLink Genetics, Johnson & Johnson and Bavarian Nordic. Another company, Emergent BioSolutions, is a contestant for manufacturing new doses of ZMapp, a drug for Ebola virus disease treatment originally developed by Mapp Biopharmaceutical. Supplies of ZMapp ran out in October 2014.
