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Advancing an effective vaccine to prevent Lassa fever in West Africa through innovation and collaboration.


Lassa fever is an acute viral hemorrhagic illness endemic to West Africa which causes significant annual outbreaks of disease. It was first identified fifty years ago, when two missionary nurses became ill and died in the town of Lassa, Nigeria. Lassa fever is zoonotic, transmitted to humans via contact with food or household items contaminated with rodent urine or faeces. Person-to-person infection can also occur, particularly in hospitals where infection control is poor. 


Lassa fever is difficult to diagnose, and surveillance data is limited and disputed. While the current disease burden is underestimated, there are an estimated 300,000 to 500,000 cases and 5,000 related deaths each year. Despite this disease burden, no vaccine for Lassa fever is currently available. One in five infections result in severe disease, where the virus affects several organs, such as the liver, spleen, and kidneys. Among patients hospitalized with severe cases, the fatality rate is 15% and deafness occurs in 25% of patients who survive.

Pregnant women are at particular risk from the disease. Among women who contract Lassa fever during the third trimester of pregnancy, more than 80% of cases result in the death of either mother or child. Death usually occurs within two weeks of the disease first appearing. In many countries where Lassa fever is endemic, women also suffer from limited access to adequate health services, exacerbating the risks they face.


LEAP4WA is part of CEPI’s recently launched $3.5 billion plan to tackle future epidemics and pandemics, which includes the goal of advancing clinical trial capacity, infrastructure, and expertise in low- and middle-income countries. The forward-looking plan also aims to advance a Lassa vaccine to licensure within the next five-year period (2022-2026).

The antiviral drug ribavirin can treat Lassa fever if given early, but there is currently no vaccine, and prevention currently relies on promoting hygiene and infection control. Pregnant women who become infected with the virus can be treated with drugs but run a high risk of losing either their own lives or those of their unborn children.

The World Health Organization has identified Lassa Virus as one of the top emerging pathogens likely to cause severe outbreaks in the near future, including it on the WHO R&D Blueprint list of epidemic threats needing urgent R&D action. In 2018, WHO published a roadmap calling for vaccine R&D to be prioritized, but vaccine R&D remains seriously underfunded. It also represents a potential bioterror threat, making further health research on this disease all the more important.


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