Fast facts about IAVI’s contributions to fighting Lassa fever in West Africa

IAVI and partners in Nigeria, Liberia, and Ghana are currently vaccinating volunteers in the Phase 2a IAVI C105 clinical trial of IAVI’s Lassa virus (LASV) vaccine candidate. The study is designed to evaluate the vaccine candidate’s safety, tolerability, and immunogenicity at two different dosage levels in adults.  

Read more about how we are contributing to the fight against Lassa fever:   

Fast facts

• LASV is the causative agent of Lassa fever, a viral hemorrhagic fever endemic to West Africa in the Arenaviridae family of highly pathogenic viruses. It is featured in the World Health Organization (WHO) Pathogen Prioritization framework as needing urgent research and development, and as a prototype pathogen for the Arenavirus family. 
• The current disease burden is underestimated. Conservative figures estimate up to 500,000 cases and at least 5,000 related deaths each year.  
• While no vaccine is available and therapeutic options remain severely limited, several vaccine candidates are currently in development. 
• IAVI’s LASV vaccine candidate is a single-dose formulation based on the modification of an attenuated or weakened strain of vesicular stomatitis virus – which is re-engineered to display the LASV surface protein that plays an essential role in establishing a viral infection.  
• Trials are being conducted in partnership with organizations including the Nigeria Centre for Disease Control and Prevention and the Nigeria Lassa Vaccine Taskforce. 
• IAVI’s LASV vaccine candidate is the most advanced and is being developed alongside partners in West Africa, Europe, and the U.S. The vaccine candidate is funded by Coalition for Epidemic Preparedness Innovations (CEPI) and the European & Developing Countries Clinical Trials Partnership (EDCTP), including work under the multidisciplinary Lassa Fever Vaccine Efficacy and Prevention for West Africa (LEAP4WA) collaboration. 
• IAVI is sponsoring the world’s first-ever Phase 2a LASV vaccine clinical trial (NCT05868733). The trial involves diverse populations, including people living with HIV, adolescents, and children two years of age and older, at clinical research partner sites in Nigeria, Liberia and Ghana. Around 612 participants will receive one dose and be followed for six months to monitor safety and immune responses. A subset will receive extended monitoring for an additional two years. 
• In September 2025, West African health ministers pledged their joint commitment to advance the development of, and readiness for, much-needed vaccines against LASVr, including IAVI’s candidate, through collectively establishing a new model to advance the equitable development and supply of vaccines targeting diseases where there is no commercial incentive for private, for-profit companies to invest. 
• We are pursuing fast, flexible manufacturing solutions. For example, in partnership with the Institut Pasteur de Dakar (IPD) in Senegal, we’re prioritizing the manufacturing and commercialization of and access to IAVI’s LASV vaccine candidate, with the potential to advance additional EID vaccine candidates, including multivalent vaccines.   
• Positive interim results from the IAVI-sponsored Phase 1 clinical trial (NCT04794218) in the U.S. and Liberia found the vaccine candidate to be safe and immunogenic. Preclinical challenge studies show that 100% of vaccinated animals were protected from infection. These results together provide strong rationale for further clinical development. 
• Should the candidate be found to be safe and efficacious in clinical testing, IAVI and our partners are committed to making the vaccine affordable and accessible to all populations in need.  
• IAVI is helping to strengthen the capacity of clinical research partner sites. These efforts further seek to increase the scientific knowledge of how the rVSV platform can be applied to address other high-priority emerging pathogens. 
• IAVI led the Wellcome-funded X100 epidemiology study in Sierra Leone, the largest-ever study of LASV incidence in the country, to support site selection for upcoming efficacy trials. 
• IAVI has been developing rVSV vaccines for more than 20 years and has been developing rVSV-based vaccines for EIDs since 2018. 
• All IAVI EID vaccine candidates use the same rVSV vector as ERVEBO^®, Merck’s single-dose Ebola Zaire vaccine that is licensed in more than a dozen countries. 
• The Public Health Agency of Canada (PHAC) provided IAVI with a nonexclusive license to the recombinant vesicular stomatitis virus (rVSV) vaccine candidates. The vector was developed by scientists at PHAC’s National Microbiology Laboratory. 
• IAVI is developing all our EID vaccines and clinical trials together with experts in endemic countries and a range of partners in the U.S. and Europe.