First-in-Human Clinical Trial Has Promising Results for New Lassa Fever Vaccine
Researchers at the 91大神 School of Medicine’s (UMSOM) reported encouraging results from an early clinical trial that tested a new dual vaccine against Lassa fever and rabies. The study, published today in the journal , found that the vaccine was safe and induced immune responses against both viruses. There are currently no vaccines against Lassa fever on the market.
The World Health Organization has identified Lassa virus as a public health threat in western Africa and made Lassa fever a priority disease for research. Like Ebola, it can trigger severe illness and periodic outbreaks in African nations. Lassa virus infections occur in 300,000 people every year resulting in 5,000 deaths, according to the , but these numbers are likely an underestimate due to limited surveillance. The disease is particularly dangerous in pregnancy with over 80 percent of late-term infections resulting in deaths to the mother or fetus.
Additionally, regions where Lassa fever is common, such as parts of Western and sub-Saharan Africa, also have a high burden of rabies, with thousands of deaths annually, a disease that is almost always fatal once symptoms develop.
Justin Ortiz, MD, MS
“This vaccine is designed to protect against two viruses of global health importance,” said study principal investigator Justin Ortiz, MD, MS, professor of medicine at UMSOM and vaccine researcher at CVD. “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.”
In this randomized, controlled trial, 54 healthy adult volunteers from the Baltimore area were randomly assigned to receive different doses of the investigational vaccine, LASSARAB, with an adjuvant or a licensed rabies vaccine control. Participants received two vaccine doses 28 days apart. Immune responses were studied through 61 days post-vaccination for an interim analysis. The results indicate that LASSARAB was safe with no serious adverse events reported after vaccination. Additionally, the candidate vaccine induced rapid and robust antibody responses against both Lassa and rabies viruses compared to the control, which only induced an immune response against rabies virus. This study is ongoing, and vaccine safety and immune responses will be further studied through 394 days post-vaccination. If the results indicate continued elevated immune responses from vaccination, researchers will proceed with more advanced clinical trials.
“This study highlights CVD’s commitment to tackling diseases of global significance,” added Stefan Kappe, PhD, director of CVD and the Myron M. Levine Endowed Professor of Pediatrics. “LASSARAB not only targets diseases of concern but utilizes a platform that could make distribution attainable in the areas of the world that are most affected by these diseases.”
This first-in-human trial was designed to evaluate the safety and immunogenicity of an adjuvanted inactivated rabies virus expressing the Lassa virus glycoprotein complex on the surface of the virus. LASSARAB was developed by a research team at Thomas Jefferson University led by Professor Matthias Schnell, director of the . Importantly, this investigational vaccine can be freeze-dried for storage, enabling distribution to areas of the world where it may be difficult to maintain cold chains.
“Environmental shifts are causing Lassa fever to extend its reach far beyond its Nigerian and West African origins, putting an estimated 700 million people at risk worldwide,” said UMSOM Dean Mark T. Gladwin, MD. “By 2070, the number of countries across Africa that will develop ecological conditions suitable for Lassa virus spread could drastically increase, so a vaccine to prevent this deadly infection is desperately needed.”
Last year, before results were available, the trial was highlighted by Nature Medicine in its 2025 feature, “,” which identified studies to watch based on their potential to address major unmet health needs.
To learn more about this and other CVD clinical trials, visit .
The study was funded by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under contract HHSN272201700082C with Thomas Jefferson University with CVD as a subcontractor. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
