World Immunization Week 2015

Ebola vaccines

The last week of April each year is the World Health Organisation Immunization Week. Clinical trials are an essential part of vaccine development and The Jenner Institute has been involved in a fast-tracked Ebola Phase I clinical trial in response to the Ebola outbreak in West Africa.

NDM spoke to Dr Katie Ewer, a Senior Immunologist involved in this trial, about the need for an Ebola vaccine and what the next steps are. 

Katie Ewer
Dr Katie Ewer

Q: Why is there currently no licensed vaccine for Ebola?

Katie Ewer: Until the recent outbreak, cases of Ebola were relatively rare compared to diseases such as malaria, which kills over 600,000 people each year. In comparison the current Ebola outbreak has killed around 23,000 people. Although Ebola is a highly fatal disease, as it isn’t very common it had not been seen as a priority for vaccine developers.

Q: How does the Ebola vaccine that was trialled in the Jenner Institute work?

KE: The Ebola vaccine that we trialled was a viral vectored vaccine, which means that 2 harmless viruses are used as vehicles to deliver a small part of the Ebola virus to the immune system. We take an adenovirus (usually responsible for the common cold), and then engineer it so that it cannot reproduce.  Next we insert a single gene from the Ebola virus. We then do the same thing with a virus called MVA. When these viruses are administered to humans a few weeks apart, the immune system produces a response to the Ebola protein, which will hopefully protect against infection and disease. This vaccination approach has been used successfully for several other disease, most notably malaria.

EVV
A single gene from the Ebola virus is transferred using DNA technology into the genetic material of the adenovirus vector. When administered to a volunteer, the adenovirus produces the protein from the gene along with its own proteins. The human immune system responds to the protein making immune cells and antibodies against teh Ebola virus. If the person then encounters the real Ebola virus, the immune system will recognise that single protein and the immune cells and antibodies will destroy the infection before the person becomes ill.

Q: What is a Phase I clinical trial and why is it necessary?

KE: A Phase I clinical trial is small-scale safety study that is used to look at different doses and to identify side effects. It also provides preliminary immunogenicity data, which indicates the type and magnitude of the immune response in humans. It is necessary to check that there are no unforeseen side-effects of the vaccine and that it generates a good immune response, before larger-scale studies to test the effectiveness of the vaccine can begin.

Q: What are the next steps in developing an Ebola vaccine?

KE The next steps are to design clinical trials to test the effectiveness of the vaccine in people that have been exposed to the virus in West Africa. These trials are very complex to design and logistically difficult to organise, but will hopefully reveal that the vaccine can protect humans against the Ebola virus disease.

At the moment, the only evidence we have for the type of immune response that will protect people from Ebola is from an experiment in monkeys. The monkeys were vaccinated and then infected with the Ebola virus. The vaccine protected the monkeys from developing Ebola. The immune responses of the monkeys were analysed to see how the vaccine worked. We hope that if we can induce the same type of immune responses (antibodies and cytokine-secreting T cells), at the same sort of levels as those seen in the monkeys that were protected against Ebola by the vaccine, that there will be a good chance that humans will also be protected. However until we test the vaccine in the areas where Ebola is still present, we won’t know for sure.