In early 2018, Nigeria has witnessed an unprecedented LF outbreak, whereby the usual annual observed LF burden has been concentrated into one trimester. From 1st January to 29th April 2018, a total of 1878 suspected cases have been reported from 21 states. Of these, 420 were confirmed positive.
The endemicity of LASV in West-Africa, the repeated occurrence of outbreaks and the recent unprecedented large LF outbreak in Nigeria have highlighted the potential for Lassa vaccines for prevention and/or reactive use. The WHO R&D Roadmap of LF identifies the following strategic goal: “develop, evaluate, and license affordable LASV vaccines that protect against the multiple LASV lineages for preventive and reactive/outbreak use in Lassa fever endemic and at-risk areas”.
Based on that goal, a WHO Lassa vaccine Target Product Profile was in 2017 developed to provide aspirational guidance to vaccine developers, and is informed by regulatory expectations and by technological feasibility and considers both a preventive and a reactive scenario for the use of a Lassa vaccine. A preventive use vaccine is intended for protection of populations living in areas where Lassa virus is endemic. A reactive use vaccine is intended for protection of at-risk persons in the area of an ongoing outbreak for the prevention of LF as well as to interrupt chains of virus transmission and to terminate outbreaks.
The WHO mapping tool currently registers 15 Lassa candidate vaccines, developed by private or public stakeholders. None of those candidates have entered clinical trials.
On April 24, 2018, WHO convened a group of about 30 experts in epidemiology, regulatory, preclinical and clinical vaccine trials, and mathematical modelling, in a workshop on planning for Lassa vaccine efficacy trials. The workshop aimed to define generic principles on how to best design, conduct and analyse vaccine trials against LF, based on the available scientific evidence as well as on lessons learned from the public health response to LF outbreaks.
According to the R&D Blueprint processes, conclusions of the R&D Roadmap of LF and the WHO Lassa vaccine Target Product Profile were expected to help inform vaccine evaluation decisions during the workshop. Participants reviewed available evidence on Lassa epidemiology and vaccine candidates, identified and discussed methodological options to evaluate vaccines, regardless of vaccine products, and agreed on some preliminary recommendations.