Trials on three separate vaccine regimens for the Ebola virus have returned positive results on their safety, promising an adequate roll-out of inoculation campaigns against one of the deadliest viral diseases.

The results from a large-scale randomised clinical trial on one of the candidate vaccines in West Africa also showed that the vaccine is capable of 12 months of protection against the viral disease.

Ebola epidemics occur periodically in various sub-Saharan Africa countries, particularly in West Africa, Central and East Africa including in DR Congo, Uganda and South Sudan.

“While vaccines exist and have already received World Health Organisation Prequalification against the Zaire ebolavirus species, it is essential to pursue and intensify efforts to supplement the available data to develop a safe and effective Ebola vaccine strategy in adults and children alike,” the PREVAC international consortium, which includes scientists from Inserm and from institutions in Africa, USA and UK; said in published results in the New England Journal of Medicine.

In a context where countries at times face Ebola outbreaks, vaccines are a central tool to fight spread of the disease.

Since 2019, two vaccines have obtained WHO Prequalification against the Zaire ebolavirus species including the vaccine rVSVΔG-ZEBOV-GP developed by Merck, Sharpe & Dohme, Corp., and the Ad26.ZEBOV and MVA-BN-Filo vaccine regimen from Johnson & Johnson.

“Beyond these advances, research on Ebola vaccines must continue. Indeed, additional data is needed in order to establish the most appropriate recommendations regarding the use of these vaccines, in different categories of the population,” said the team.

The trial testing three vaccine regimens is one of the largest Ebola vaccination trials to date – conducted with both adults and children including 1,400 adults and 1,401 children aged one year and older.

Participants will be followed up over a five-year period to assess the long-term safety of vaccines and the durability of the immune response. Such data will shed light on whether it is necessary to provide a vaccine booster to individuals who are already vaccinated.

It aimed to measure the rapidity, intensity and durability of the immune responses generated by the three different Ebola vaccine regimens. It also evaluated the safety and tolerability of the various products administered.

The data obtained so far suggest that all three regimens are safe and well-tolerated in adults and children. After vaccination and within the seven days that followed, the majority of the participants reported pain at the injection site and other minor symptoms (fever, muscle and joint pain, headache, etc.), which generally disappeared after seven days.

Strong partnerships

The three regimens also generated a rapid increase, after 14 days, of the number of antibodies directed against the virus, with a peak at between 1 and 3 months after the first vaccination. While it’s not yet possible to say whether this immune response prevents infection, current scientific literature suggests a strong correlation between the amount of these antibodies and the level of protection against the virus. These antibodies were detected up to 12 months after the first injection.

“The data collected are valuable because they help confirm the safety and potential efficacy of the available vaccines, making it possible to refine the vaccination recommendations during both Zaire ebolavirus epidemic and inter-epidemic periods, in populations at risk,” the trial’s principal investigator, Yazdan Yazdanpanah said.

“This trial had high participant retention thanks to the unwavering involvement of all the professionals in the field, and the population’s adherence to research that led to these results,” principal investigator Mark Kieh said.

“The PREVAC trial is a real example of success for international research in emerging and re-emerging infections. With strong partnerships, we can advance Ebola research in the areas most affected by the disease,” emphasised Clifford Lane, NIAID Deputy Director for Clinical Research and Special Projects.