Lassa Fever Tracker 2026
About Lassa Fever
What is Lassa fever?
Lassa fever is a viral haemorrhagic illness, in the same broad family of severe diseases as Ebola, that is endemic in parts of West Africa — especially Nigeria. It is carried by a common rodent, the multimammate rat. Most people catch it by eating food or touching surfaces contaminated with the urine or droppings of infected rats. It can also spread between people through direct contact with the body fluids of someone who is sick, which puts caregivers and healthcare workers at particular risk.
What are the symptoms?
About 8 in 10 infections are mild or cause no symptoms, so many cases go undetected. When symptoms do appear — usually 6 to 21 days after exposure — they start with fever, weakness, headache, and sore throat, and can progress to vomiting, muscle pain, bleeding, and, in severe cases, organ failure. One of the most common long-term complications in survivors is hearing loss, which can be permanent. The disease is especially dangerous in pregnancy, where late-term infection very often results in the loss of the baby.
How is it treated?
The antiviral drug ribavirin is the main treatment and works best when started early, which is why rapid testing and diagnosis are so important. Supportive care — fluids, oxygen, and treating complications — also improves the odds of survival. There is currently no approved vaccine, though several candidates are in clinical trials (see below).
Sources: WHO Lassa fever fact sheet · NCDC Lassa fever · Africa CDC
Treatments & Vaccines in Development
Lassa fever has no approved vaccine yet, but it is a WHO priority disease and several candidates — including a novel dual Lassa-and-rabies shot — are now in human trials. Here's where the science stands.
The antiviral ribavirin is the current standard treatment for Lassa fever. It works best when started early in the illness, which is why fast diagnosis matters so much. It is not a cure and evidence for its benefit is limited, but it remains the main specific therapy alongside supportive care.
WHO Lassa fever fact sheet →A first-in-human trial of this dual vaccine — designed to protect against both Lassa and rabies from a single shot — found it safe and showed it triggered antibody responses against both viruses in 54 healthy adults. It uses an inactivated rabies platform and can potentially be freeze-dried, which would ease distribution in areas without reliable cold chains. The study is ongoing through 394 days before moving toward larger trials.
News-Medical / Nature Medicine, July 2026 →IAVI's Lassa vaccine candidate showed durable immune responses and an acceptable safety profile in a Phase 1 study, with results published in the New England Journal of Medicine. It uses the same viral-vector approach as the approved Zaire Ebola vaccine.
IAVI →A measles-virus-vectored Lassa vaccine candidate, one of several supported by CEPI (the Coalition for Epidemic Preparedness Innovations) as part of a broader push to have a Lassa vaccine ready for outbreaks.
CEPI →A DNA-based Lassa vaccine that completed a Phase 1b trial in Ghana with promising immune responses (published 2025). However, Inovio discontinued active development of this candidate, so it is not currently advancing toward approval.
Frontiers in Immunology →