The clinical trial of a Lassa fever candidate vaccine has begun enrolling participants at the University of Maryland School of Medicine, Baltimore. Lassa virus (a member of the Arenavirus family) causes Lassa fever, a severe hemorrhagic disease that can be fatal and 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 and outbreaks in that region are increasing. The virus can also be spread from person to person.
Currently, there are no specific drug treatments or vaccines for Lassa fever, which is on the World Health Organization’s (WHO) Priority Pathogen list. NIH’s National Institute of Allergy and Infectious Diseases (NIAID) is sponsoring the Phase I trial (NCT06546709).
“The candidate vaccine 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. “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.”
LASSARAB is a deactivated rabies virus (RABV)-based vaccine encoding the glycoprotein precursor (GPC) of Lassa fever virus. 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 an FDA-licensed rabies vaccine (control).
In research published in 2024, Matthias Schnell, PhD, and colleagues at Thomas Jefferson University tested the experimental LASSARAB vaccine 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. This work was published in npj Vaccines in the article, “Inactivated rabies-based Lassa fever virus vaccine candidate LASSARAB protects nonhuman primates from lethal disease.”
In August of 2024, IAVI’s (International AIDS Vaccine Initiative) Lassa fever vaccine candidate entered Phase II, making it the first Lassa vaccine clinical trial to become fully active across West Africa. Approximately 612 participants started to receive one dose of the candidate and will be followed for six months after vaccination to monitor their safety and immune responses. The study was designed in consultation with in-country partners and is funded by CEPI.
