In October 2024, CEPI announced the expansion of research into Lassa fever in West Africa in a “pioneering study” to explore the variation in disease symptoms and how this compares to other “worrisome infections” in the region. The project, led by the Nigeria Centre for Disease Control and local study sites, comes under the Enable study, created by CEPI and partners to provide a more accurate picture of the disease burden in West Africa and help inform outbreak preparedness efforts, including Lassa vaccine development. Lassa fever, a known public health burden in the region, infects “hundreds of thousands” every year. However, cases are likely underreported due to detection difficulties.
Lassa fever
Although it was described in the 1950s, the virus causing Lassa fever was only identified in 1969. It is a single-stranded RNA virus in the Arenaviridae family. The disease is a “potentially deadly haemorrhagic illness” with an estimated 1% case fatality rate. Most infections are thought to be “minimally symptomatic or asymptomatic”, which means they avoid detection. People who do experience symptoms can suffer fever, headache, and chills, and could be misdiagnosed with diseases like Ebola, dengue, or malaria.
As a WHO priority disease, Lassa fever is in “urgent need” of research and development. Understanding the disease is critical to vaccine development, which Dr Muhammad Ali Pate, Coordinating Minister of Health and Social Welfare of Nigeria, recognises.
“Lassa fever remains a public health burden in Nigeria and West Africa, but the commitment to research and innovation is yielding promising progress. The new Enable research will deepen our understanding of the virus and enhance the work being undertaken to develop the first-ever Lassa vaccine to safeguard the health of our communities.”
Dr Pate highlighted the Ministry’s commitment to collaboration to “advance these efforts and bring the suffering caused by Lassa fever to an end”.
Enable expanded
Enable was launched in 2019, and in 2021 CEPI announced funding to provide a “more accurate assessment” of the incidence of Lassa fever infections. CEPI offered US$ 10.3 million to partners in Benin, Guinea, Liberia, and Sierra Leone to participate, enrolling up to 23,000 participants to understand the “rate, location, and spread of Lassa virus across the region”. The results are also central to CEPI’s goal of producing a licensed Lassa vaccine.
The new year-long study will invite 5,000 healthy people, including children and infants, to participate at sites in Nigeria (Edo, Ondo, and Ebonyi states), Sierra Leone, and Liberia. It is intended to improve understanding on how commonly the disease occurs, how rates of infection and symptoms vary across locations, ages, sex, and exposure history, and the extent of post-infection symptoms. Scientists will also explore how often people are co-infected with Lassa fever and malaria, as co-infections may complicate the clinical course of each disease.
Vaccine goals
Dr Richard Hatchett, CEO of CEPI, explained that “incomplete detection” of cases affects both the understanding of the true incidence rate and level of response, but could also “threaten the evaluation, rollout, and acceptance of future Lassa vaccines”.
“Insights gained on the diversity of disease symptoms will enhance our understanding of Lassa fever, categorised into mild, moderate, or severe cases. This information will be crucial in guiding where and how future late-stage vaccine trials are conducted and determining priority groups for receiving the Lassa vaccine once it becomes licensed in the coming years.”
A 2024 modelling study found that around 3,300 lives could be saved over 10 years with a Lassa vaccine. It could also avert up to $128 million in societal costs. The most advanced vaccine candidate is developed by IAVI and is currently in Phase II trials in the region. Enable National Project Coordinator in Nigeria, Mrs Elsie Ilori, described the launch of the expanded study as a “key step in our ongoing efforts to understand and combat this dreadful disease”.
“Through deeper investigations into the variations of Lassa fever symptoms and their comparison to other infections within the region, we will obtain valuable insights that can improve diagnosis, boost outbreak preparedness, and inform the future vaccine development.”
Dr Jilde Idris, Director General of Nigeria Centre for Disease Control and co-chair of the Nigeria Lassa Vaccine Task Force agreed that the investigation “represents key progress in our battle against Lassa fever”.
“We are improving our capacity to identify and recognise cases while preparing for future vaccine development by examining the disease’s symptoms and its connection to other infections.”
The work is “vital for forming health practices” and “promoting” public health in the region, and Dr Idris welcomed the support of partners and local communities in “making strides towards lessening the impact of Lassa fever” and preparing for a “future that can block its life-threatening effects”.
For more on IAVI’s vaccine efforts and insights into challenge studies in West Africa, join us at the Congress in Barcelona this month for a session with Dr Marion Gruber. Don’t forget to subscribe to our weekly newsletters here for vaccine updates!
