A Trial to Evaluate the Safety, Immunogenicity and the Optimal Dose of MOPEVAC-Las Vaccine Candidate Against Lassa Fever

Lassa fever is an acute viral disease belonging to the category of viral hemorrhagic fevers. It is endemic in West Africa. Outbreaks occur every year, and it is estimated that between 100 000 and 300 000 individuals are infected each year, with a fatality rate for symptomatic cases that ranges between 15 and 30%. There is no efficient treatment against the disease, as ribavirin, the only licensed therapy, is at best poorly efficient. MOPEVAC-Las is a live-attenuated vaccine candidate targeting Lassa virus. The objective of this phase 1 clinical trial is to evaluate the safety of the MOPEVAC-Las vaccine candidate on healthy volunteers. It will also evaluate the immunogenicity and optimal dose of the vaccine candidate. The main questions it aims to answer are: * What are the safety and tolerability of the MOPEVAC-Las vaccine candidate following two intramuscular injections in healthy volunteers ? * Are cell-mediated immunity and humoral immunity induced by the MOPEVAC-Las vaccine ? * What is the optimal dose of MOPEVAC-Las vaccine regarding safety, tolerability and immunogenicity ? Researchers will compare the MOPEVAC-Las vaccine candidate to a placebo (a look-alike substance that contains no drug).