On a Baltimore afternoon in 2025, researchers at the University of Maryland School of Medicine announced a breakthrough that could reshape the fight against two of the world's deadliest viruses: a single vaccine that protects against both Lassa fever and rabies. Published in Nature Medicine, the early-stage trial of LASSARAB marks the first time a human has received this dual-action shot—and lived to tell about it, with no serious adverse events recorded.
This matters because Lassa fever kills without warning and without mercy. The World Health Organization has classified it as a priority disease, particularly in West Africa, where approximately 300,000 people become infected each year, resulting in some 5,000 deaths according to the Africa Centers for Disease Control and Prevention—though actual numbers are almost certainly higher due to gaps in surveillance. The disease is especially brutal in pregnancy, claiming the life of the mother or fetus in more than 80% of late-term infections. Yet despite its devastation, there is currently no licensed vaccine against Lassa fever anywhere on the market. The regions most burdened by Lassa are also ravaged by rabies, which is almost always fatal once symptoms appear.
Enter Justin Ortiz, MD, MS, professor of medicine at the University of Maryland School of Medicine and principal investigator on the trial. Ortiz and his team at the Center for Vaccine Development and Global Health enrolled 54 healthy adults from the Baltimore area and gave them two doses of LASSARAB, spaced 28 days apart. Half received the experimental vaccine with an adjuvant designed to boost immune response; the control group received a licensed rabies vaccine. When researchers checked in at 61 days post-vaccination, the results were striking: LASSARAB generated rapid and robust antibody responses against both viruses, far outpacing the control group's response to rabies alone. Safety data showed no serious adverse events.
The vaccine's design holds clues to its broader potential. Developed by Matthias Schnell's team at Thomas Jefferson University, LASSARAB works by engineering an inactivated rabies virus to display the Lassa virus glycoprotein on its surface—essentially training the immune system to recognize both threats simultaneously. Crucially, the vaccine can be freeze-dried for storage, a feature that could prove transformative in resource-limited settings where maintaining cold chains is logistically impossible. This is not a small detail in regions where electricity is unreliable and distances vast.
The timing could not be more urgent. Mark T. Gladwin, dean of the University of Maryland School of Medicine, noted that climate change is extending Lassa fever's reach far beyond Nigeria and West Africa, putting an estimated 700 million people at risk globally. By 2070, ecological conditions suitable for Lassa virus spread could emerge across dramatically more of Africa.
The trial is ongoing, with researchers monitoring participants through 394 days post-vaccination. If immune responses remain elevated, the vaccine advances to larger, more rigorous clinical trials. "By combining targets into a single product, it could reduce the need for separate vaccination efforts and streamline delivery in settings where access is limited," Ortiz said. In places where disease runs unchecked and resources are stretched thin, that efficiency—one shot instead of two, freeze-dried rather than refrigerated—could mean the difference between vulnerability and protection for millions.