Lassa Fever

Lassa fever is a severe viral hemorrhagic illness endemic to West Africa, caused by the Lassa virus—a pathogen designated as a Federal Select Agent due to its epidemic potential and relevance to national and global health security. The virus is primarily transmitted to humans through contact with the urine or feces of infected rats, with limited but significant potential for person-to-person transmission, particularly in healthcare settings lacking proper infection prevention and control.

While most Lassa virus infections are mild or asymptomatic, approximately 20% develop severe disease involving multi-organ dysfunction, with case fatality rates exceeding 15% among hospitalized patients. The risks are especially high for pregnant women, with third-trimester infections often resulting in near-total fetal loss and high maternal mortality. Sudden-onset deafness and long-term neurological sequelae are common among survivors.

Lassa fever has been prioritized by the WHO for accelerated research and development of medical countermeasures—including more reliable diagnostics, effective therapeutics, and safe, scalable vaccines. There is currently no licensed vaccine and ribavirin, the only available antiviral, has uncertain efficacy.

Explore our latest articles to stay informed on the evolving science, policies, and innovations shaping the Lassa fever response.