Thursday, March 26, 2015

New Ebola Vaccine Found Safe In Early Human Trials

New Ebola Vaccine Found Safe In Early Human Trials


Since its first outbreak occurred in 1976, Zaire Ebola virus have been associated with 14 outbreaks reported up to 2014. Ebola viruses are enveloped, non-segmented, negative-strand RNA viruses belonging to the family of Filoviridae. Five different species of Ebola virus have been identified: Zaire, Sudan, Côte d'Ivoire, Reston, and Bundibugyo. The Zaire Ebola virus in 2014 causing the most serious outbreak was considered to be a new epidemic strain, with GP homology of the gene was only 97.6%, compared to the GP gene of the strain in 1976.

Five different species of Ebola virus have been identified

Researchers have developed an investigational Ad5-EBOV vaccine was developed according to the 2014 epidemic Zaire strain and formulated as freeze-dry products which could be stored at 4℃.

Result show that the high-dose vaccine is safe and robustly immunogenic


Researchers carried a randomised, double-blind, placebo-controlled, phase 1 clinical trial at one site in Taizhou County, Jiangsu Province, China. Healthy adults (aged 18–60 years) were sequentially enrolled and randomly assigned (2:1), by computer-generated block randomisation (block size of six), to receive placebo, low-dose adenovirus type-5 vector-based Ebola vaccine, or high-dose vaccine. Randomisation was pre-stratified by dose group. All participants, investigators, and laboratory staff were masked to treatment allocation. The primary safety endpoint was occurrence of solicited adverse reactions within 7 days of vaccination. The primary immunogenicity endpoints were glycoprotein-specific antibody titres and T-cell responses at day 28 after the vaccination. Analysis was by intention to treat. The study is registered with, number NCT02326194.


Result show that the high-dose vaccine is safe and robustly immunogenic. One shot of the high-dose vaccine could mount glycoprotein-specific humoral and T-cell response against Ebola virus in 14 days. 

The adenovirus type-5 Ebola virus has a good safety profile in healthy adults. The incidence of adverse reactions was in line with findings from previous studies of other viral-vectored Ebola vaccines. A significantly higher incidence of pain at the injection site was noted in participants in the high-dose vaccine group, probably because of a high dose of viral particles. But almost all the reported adverse reactions or events were mild or moderate, and the high-dose vaccine was still well tolerated.

The magnitude of the immune response to the vaccine was dose-dependent. Ebola glycoprotein-specific antibody was significantly increased by day 14, and continued to increase up to day 28 after the vaccination, whereas the Ebola glycoprotein-specific T-cell responses peaked at day 14. 

However, both vaccine-elicited Ebola glycoprotein-specific antibody response and T-cell response were partly blunted by the presence of pre-existing anti-adenovirus type-5 immunity, especially in participants in the low-dose group. 

The high-dose vaccine could overcome the negative effects of pre-existing immunity and still induced robust Ebola glycoprotein-specific antibody and T-cell responses in participants with a high baseline concentration of neutralising antibody. Because a large proportion of adults have pre-existing adenovirus type-5 immunity, especially in developing countries, a high dose of the viral particles would seem necessary.

Article citation: Chen, W.; et. al. Safety and immunogenicity of a novel recombinant adenovirus type-5 vector-based Ebola vaccine in healthy adults in China: preliminary report of a randomised, double-blind, placebo-controlled, phase 1 trial. Lancet 2015DOI: