Clinical trial of vaccine candidate to prevent Lassa fever begins enrollment

A National Institutes of Health (NIH)-sponsored clinical trial of a candidate vaccine to prevent Lassa fever has begun enrolling participants at the University of Maryland School of Medicine, Baltimore. Lassa fever is a viral hemorrhagic disease that can be fatal and that causes permanent hearing loss in up to one-third of those who contract it. Lassa virus is spread by rodents, known as multimammate rats, that are native to many countries in West Africa. The virus can also be spread from person to person. Currently, there are no specific drug treatments or vaccines for Lassa fever. NIH's National Institute of Allergy and Infectious Diseases (NIAID) is sponsoring the Phase 1 trial.

The candidate vaccine being tested in this trial was developed by an NIH-supported research team at Thomas Jefferson University in Philadelphia. The progression of this candidate from the lab to a first-in-humans clinical trial is a promising step towards a vaccine to prevent Lassa fever." 

Jeanne Marrazzo, M.D., M.P.H., NIAID Director 

The trial will enroll up to 55 healthy adults between the ages of 18 and 50 years to test the safety and immunogenicity of three different concentrations of the vaccine candidate. Participants will receive two injections, delivered 28 days apart, of either the vaccine candidate or a Food and Drug Administration-licensed rabies vaccine (control).

In research published in 2024, Matthias Schnell, Ph.D., and colleagues at Thomas Jefferson University tested the experimental vaccine, known as LASSARAB, in nonhuman primates. They found that two doses of the vaccine, delivered 28 days apart, protected all the immunized animals that were 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 subsequently inactivated to make the vaccine candidate. The experimental vaccine is then modified so that it expresses all the rabies proteins found in inactivated rabies vaccine along with a Lassa virus surface protein called the glycoprotein precursor complex (GPC). If LASSARAB is shown to be 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 approval by the FDA.

Additional information about the new clinical trial is available at clinicaltrials.gov using the identifier NCT06546709.