FAST FACTS
Lassa virus (LASV) is the causative agent of Lassa fever, a viral hemorrhagic fever endemic to West Africa, and is the highest priority potential bioweapon.
IAVI and partners in Ghana, Liberia, and Nigeria are currently vaccinating volunteers in the IAVI C105 clinical trial of IAVI’s 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 IAVI and partners are contributing to the fight against Lassa Fever:
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Lassa fever is endemic throughout much of West Africa, causing (by one estimate) up to 2.7 million infections and several thousand deaths each year.
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Increasingly, Nigeria is experiencing severe annual outbreaks, typically occurring between December and March. Most recently, the Nigeria Centre for Disease Control and Prevention (NCDC) raised the alarm in December 2024 over a spike in Lassa fever infections, with 1,154 confirmed cases and 190 deaths recorded during the year. By the end of 2024, the death toll had increased to 214 out of 1,309 confirmed cases. In the first six weeks of 2025, another 1913 suspected cases, 413 confirmed cases and 80 deaths had been reported, according to NCDC data.[i]
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While patients can sometimes be treated with antiviral drugs, no licensed vaccine is currently available. A recent study by the University of Oxford estimated that vaccinating high-risk populations against Lassa Fever virus could avert up to 4,400 deaths in West Africa and save societal costs, including labor losses and healthcare, of almost US$129 million a year.[ii]
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Several vaccine candidates are in development. One of these is IAVI’s rVSVΔG-LASV-GPC, which is currently being developed by IAVI and partners, with funding from CEPI and the European & Developing Countries Clinical Trials Partnership (EDCTP).
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IAVI’s vaccine candidate is a single-dose vaccine formulation, based on the modification of an attenuated or weakened strain of vesicular stomatitis virus (VSV), which is then re-engineered to display the LASV surface protein that plays an essential role in establishing a viral infection and stimulating immunity.
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The same VSV vector platform has already been used to create ERVEBO®, Merck’s single-dose Ebola virus vaccine, which has been widely licensed as safe to use in more than a dozen countries, and which has already been used to control Ebola outbreaks in the Democratic Republic of Congo. IAVI has been developing rVSV vaccines for more than 20 years and has been developing rVSV-based vaccines for EIDs since 2018. Learn more about how VSV vaccines work.
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IAVI C105 aims to study the vaccine in diverse populations, including people living with HIV, as well as adolescents and children two years of age and older. Approximately 612 participants will receive one dose of the candidate and will be followed for six months after vaccination to monitor their safety and immune responses. A subset of participants will be followed for an additional two years for extended safety and immunogenicity.
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Trials are being conducted in partnership with organizations including the Nigeria Centre for Disease Control and Prevention and the Nigeria Lassa Vaccine Taskforce.
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Should the candidate be found to be safe and efficacious in clinical testing, IAVI and our partners are committed to making its Lassa Fever vaccine affordable and accessible to all populations in need.
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In partnership with the Institut Pasteur de Dakar (IPD), IAVI is prioritizing the manufacturing and commercialization of rVSVΔG-LASV-GPC, with the potential to advance additional EID vaccine candidates, including multivalent vaccines.
[i] https://www.gavi.org/vaccineswork/health-workers-face-down-mortal-risk-lassa-fever-spikes-nigeria