An experimental vaccine that could protect against two deadly diseases with a single injection has shown encouraging results in its first human trial. The vaccine, called LASSARAB, is designed to prevent both Lassa fever and rabies, two viral threats that overlap in parts of West Africa where access to healthcare is limited.
In a Phase 1 trial involving 54 healthy adults aged 18 to 50, researchers found that 100 percent of participants who received LASSARAB developed Lassa virus-specific antibodies within 61 days of the first dose. At the same time, all recipients achieved neutralizing antibody levels against rabies that exceeded the World Health Organization’s threshold for protection, matching the immune response seen with licensed rabies vaccines. No serious adverse events were reported, and side effects such as injection-site tenderness and mild flu-like symptoms were temporary and resolved without treatment.
Lassa fever causes an estimated 300,000 to 500,000 infections and more than 5,000 deaths each year in West Africa, leading to severe complications including organ failure, hearing loss and long-term neurological disorders. Currently, no licensed vaccine exists for Lassa fever. LASSARAB is built on an inactivated rabies virus vector engineered to express a key protein from the Lassa virus, combined with a synthetic adjuvant to boost immune response. This approach leverages the rabies vaccine’s established safety record, durable immunity and existing global manufacturing and distribution networks. Among three Lassa fever vaccines in development, LASSARAB is the only one based on a killed or inactivated virus.
What This Means for Global Health
“These results provide the first clinical evidence that a rabies-vectored platform can safely generate immunity to Lassa virus in humans,” said senior author Matthias J. Schnell, PhD, director of the Jefferson Center for Vaccines and Pandemic Preparedness. “The ability to combine protection against Lassa fever and rabies in a single vaccine could have a substantial public health impact in regions where both diseases remain endemic.” The trial was conducted by researchers from Thomas Jefferson University and the University of Maryland School of Medicine and published in Nature Medicine.
Because this was an early-stage trial focused on safety and immune response, not efficacy, researchers caution that longer follow-up and larger studies in Lassa-endemic populations are needed to confirm durability and real-world effectiveness. Still, the findings support continued development of LASSARAB as a next-generation, dual-purpose vaccine. If successful in future trials, a single shot could one day help protect millions of people against two major threats, offering a practical and scalable solution for resource-limited regions.