Liberia: PREVAIL Part of Large Ebola Vaccine Study Conducted  in West Africa That Publishes Promising Findings  


MONROVIA – The Partnership for Research on Vaccines and Infectious Diseases in Liberia (PREVAIL), a joint Liberia-United States clinical research partnership, is part of the Partnership for Research on Ebola Vaccinations (PREVAC), an international consortium that conducts research in West Africa. The PREVAC consortium (Liberia, Guinea, Mali, and Sierra Leone) includes scientists from PREVAIL, the French research organization Inserm, and from institutions in Africa, the United States, and the United Kingdom. The consortium has now published the results of a large clinical study in West Africa in the New England Journal of Medicine. These results confirm the safety of three different Ebola vaccine regimens and suggest that each regimen induces an immune response that is maintained for up to one year.   

Since 2017, the PREVAC international consortium has focused on implementing a multicenter, randomized, placebo-controlled, phase 2 Ebola vaccine study that mobilized African, European and US research teams working together in Liberia, Guinea, Sierra Leone, and Mali.  It is one of the largest Ebola vaccination studies to date – conducted with both adults and children aged 1 year and above. In total, the study included 1400 adults and 1401 children between 1 and 17 years of age, who were randomized into several groups to test and compare the three regimens versus placebo. In Liberia, PREVAIL enrolled 657 adults and 476 children in the study, known as PREVAIL V.

Considering Ebola outbreaks in many countries of Sub-Sahara Africa, vaccines are seen as a central tool to fight the spread of the disease. Since 2019, two vaccines have obtained WHO prequalification against the Zaire ebolavirus species: the vaccine rVSVΔG-ZEBOV-GP developed by Merck, Sharpe & Dohme, Corp., and the vaccine strategy comprised of the Ad26.ZEBOV and MVA-BN-Filo vaccines from Janssen Vaccines & Prevention, BV.

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

  • The first vaccine regimen tested consisted of one dose of Ad26.ZEBOV, followed 56 days later by one dose of MVA-BN-Filo
  • The second regimen consisted of one dose of rVSVΔG-ZEBOV-GP.
  • Finally, the third regimen started with one dose of rVSVΔG-ZEBOV-GP, followed 56 days later with the same vaccine as a booster.  

Liberia – US Joint Clinical Research Partnership

Results from this study suggest that all three regimens are safe and well tolerated in adults and children.  After vaccination and within the 7 days that followed, most participants reported pain at the injection site and also other minor symptoms (fever, muscle and joint pain, headache, etc.).  These minor symptoms disappeared generally within7 days.

After 14 days, the three regimens also generated a rapid increase in the amount of antibodies directed against the Ebola virus. The highest levels occurred between 1 and 3 months after the first vaccination. While it is not yet possible to say whether this immune response prevents infection, the 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. 

Beyond these advances, research on Ebola vaccines must continue, say the investigators. Indeed, additional data is needed to establish the most appropriate recommendations regarding the use of these vaccines in different population groups.  

“This trial is marked by a high participant retention rate, thanks to the unwavering involvement of all the professionals in the field, and the population’s adherence to the research that led to these results,” says Dr. Mark Kieh, PREVAIL Principal Investigator. 

“The data collected during this clinical trial 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,” explains the trial’s principal investigator, Dr. Yazdan Yazdanpanah of Inserm.

The PREVAC trial is an excellent example of success in emerging and re-emerging infections, as it demonstrates the effort of collaboration through strong and committed partnership, we can advance Ebola research in the areas of the world most affected by the disease,” emphasizes Dr. James Tanu Duworko, PREVAIL Director.

The work of the PREVAC consortium in West Africa continues, thanks in part to a European funding from the EDCTP supported by the European Union.Participants will be followed up over a 5-year period to assess the long-term safety of vaccines and the durability of the immune response. It is crucial to obtain such data, which will shed light, for example, on whether individuals who are already vaccinated will need a booster dose.