New Ebola vaccine safe, stimulates strong immune response

A fresh clinical trial of a new Ebola vaccine has found that it is well tolerated, safe and stimulates strong immune responses in adults in Mali, West Africa and in the US.

The study included the first testing of this vaccine in adult health care workers and other at-risk persons in Africa. It identified the dose to be used in subsequent clinical trials and for large-scale manufacture of the vaccine.

According to a global consortium of researchers assembled at the behest of the World Health Organisation (WHO), if larger trials (some already ongoing in Mali) corroborate the vaccine's clinical acceptability and immunogenicity, the vaccine can obtain regulatory approvals to become a tool to interrupt transmission in future outbreaks.

This would be achieved by vaccinating all people who have come into contact with confirmed Ebola cases. "This is a crucial step on the road to using this vaccine in humans," said Myron M Levine, associate dean for global health from University of Maryland's school of medicine.

"This gives us essential information that the vaccine is not only well-tolerated but the high dose stimulates strong immune responses in adults in West Africa, the global region where the Ebola outbreak was rampant last year," he added.

The investigators also found that the administration of a booster vaccination with another vector vaccine producing Ebola virus antigens led to further enhanced immune responses likely to be associated with long-lived protection.

This approach provides a way to vaccinate health care workers and other front-line workers who live in areas where Ebola poses a threat to re-emerge and who need prior enduring protection.

"If the vaccine is ultimately found to be safe and effective, it could offer crucial protection for contacts (family members and neighbours) of patients with confirmed Ebola disease in future epidemics, thereby helping to interrupt transmission," the authors noted.

The vaccine consists of an adenovirus (cold virus) that has been modified so that, in humans, it does not cause illness and cannot multiply. It does not contain the entire virus but a single Ebola protein.

The study compared the clinical acceptability and immune responses of 20 adult participants in Baltimore and 91 in Mali and each group was given different dosage levels of vaccine.

The study found that there were no safety concerns and recommended that further studies be carried out. (The paper was published in the latest issue of the journal Lancet Infectious Disease.)