Press release
Monday, March 17, 2025
Lassa fever is a potentially fatal viral hemorrhagic disease that causes permanent hearing loss.
Scanning electron micrograph of Lassa virus budding from a cell. Lassa virus (LASV) is an arenavirus that causes Lassa hemorrhagic fever, a type of viral hemorrhagic fever (VHF) in humans and other primates.NIAID
A National Institutes of Health (NIH)-sponsored clinical trial of a vaccine candidate to prevent Lassa fever has begun enrolling participants at the University of Maryland School of Medicine in Baltimore. Lassa fever is a life-threatening viral hemorrhagic disease that causes permanent hearing loss in up to one-third of people who contract it. The Lassa virus is transmitted by rodents known as multimammary rats, which are native to many West African countries. The virus can also be transmitted from person to person. There is currently no specific drug treatment or vaccine for Lassa fever. The NIH's National Institute of Allergy and Infectious Diseases (NIAID) is funding the Phase 1 trial.
“The vaccine candidate being tested in this trial was developed by an NIH-supported research team at Thomas Jefferson University in Philadelphia,” said NIAID Director Jeanne Marrazzo, MD, MPH. “Moving this candidate from the laboratory to a first-in-human clinical trial is a promising step toward a vaccine to prevent Lassa fever.”
The trial will enroll up to 55 healthy adults aged 18 to 50 years to test the safety and immunogenicity of three different concentrations of the vaccine candidate. Participants will receive two injections, administered 28 days apart, of either the vaccine candidate or a Food and Drug Administration-licensed rabies vaccine (control).
In a study published in 2024Matthias Schnell, Ph.D., and his colleagues at Thomas Jefferson University tested the experimental vaccine, known as LASSARAB, in nonhuman primates. They found that two doses of the vaccine, administered 28 days apart, protected all immunized animals that had been exposed to large and lethal amounts of Lassa virus six weeks after the second inoculation.
LASSARAB is based on a weakened (attenuated) rabies vaccine that is then inactivated to make the vaccine candidate. The experimental vaccine is then modified to express all of the rabies proteins present in the inactivated rabies vaccine as well as a Lassa virus surface protein called glycoprotein precursor complex (GPC). If LASSARAB proves safe and elicits a good immune response to both the rabies proteins and the Lassa GPC, it could be used to prevent both diseases pending further testing in clinical trials and subsequent FDA approval.
Additional information about the new clinical trial is available at clinicaltrials.gov with the identifier NCT06546709.
NIAID conducts and supports research—at the NIH, in the United States, and worldwide—to study the causes of infectious and immune-mediated diseases, and to develop better ways to prevent, diagnose, and treat these diseases. Press releases, fact sheets, and other NIAID-related materials are available at NIAID website.
About the National Institutes of Health (NIH): NIH, the nation's medical research agency, comprises 27 institutes and centers and is part of the U.S. Department of Health and Human Services. NIH is the primary federal agency that conducts and supports basic, clinical, and translational medical research, and studies the causes, treatments, and cures for common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
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