An inactivated rabies virus engineered to display the Lassa fever glycoprotein on its surface induced anti-Lassa IgG antibodies in every vaccinated participant who completed a two-dose primary series, according to Phase 1 results published in Nature Medicine — the first-in-human data for this rabies-vectored vaccine candidate, known as LASSARAB.
The open-label, dose-escalation study enrolled 54 healthy adults. Forty-four completed the two-dose regimen and were included in the primary immunogenicity analysis. After the second dose, 100% (44/44) developed detectable Lassa-specific IgG antibodies, with titres in the range associated with protection in non-human primate challenge models. The vaccine was well-tolerated; no serious adverse events were attributed to the investigational product.
LASSARAB uses a killed recombinant rabies virus as its vector backbone — the same fundamental platform as licensed inactivated rabies vaccines. The Lassa glycoprotein complex (GPC) insert is displayed on the surface of the inactivated particle, intended to elicit both antibody and T-cell responses to the envelope protein that mediates cellular entry. Because the vector is inactivated, LASSARAB is not a live vaccine, a property that simplifies cold-chain management and deployment in resource-limited settings.
Lassa fever affects an estimated 100,000 to 300,000 people per year in West Africa, with a case-fatality rate of approximately 15–20% among hospitalised patients. No licensed vaccine exists. The WHO has listed Lassa fever as a priority pathogen since 2017; the Coalition for Epidemic Preparedness Innovations has funded multiple candidates, of which LASSARAB is one.
Whether the IgG titres observed translate to clinical protection is not yet established. No validated immune correlate of protection exists for Lassa fever — a gap that complicates accelerated development under animal rule pathways. Phase 2 and Phase 3 trials with efficacy endpoints in endemic populations are required before regulatory filing. At least four other Lassa vaccine candidates are in clinical development, including mRNA-based approaches; the LASSARAB result strengthens the overall signal that antibody responses against Lassa GPC are achievable and well-tolerated in humans.