Deploying a safe and effective Lassa vaccine across 15 countries in West Africa could save nearly 3,300 lives over 10 years and avert up to $128m in societal costs, according to new research by modelling experts.

The peer-reviewed study, published on August 28, 2024, in Nature Medicine, is titled “Health and Economic Impacts of Lassa Vaccination Campaigns in West Africa.”

Also read: Lassa fever: NCDC records 84 deaths in seven weeks

The study suggests that vaccination against Lassa Fever, a viral disease spread by rodents and contaminated food, would prevent millions from falling ill and facing prohibitive treatment costs, which could otherwise push them below the poverty line. The research was conducted by the Universities of Oxford and Liverpool, and the Liverpool School of Tropical Medicine.

Led by David Smith of the Nuffield Department of Population Health, Health Economics Research Centre, University of Oxford, the study noted that a vaccine effective against both infection and disease would have a significantly greater impact.

The research underscores the urgent need for a vaccine to protect people from this debilitating and sometimes deadly disease, which likely affects many more people than reported due to limited access to diagnostics and healthcare.

The research team also assessed the impact of deploying a vaccine against a new Lassa-like virus with pandemic potential—a hypothetical disease they named Lassa X—within 100 days of its emergence. This was to model the potential impact of the “100 Days Mission” in the event of a future human outbreak of a Lassa-like viral disease.

The results showed that approximately 5,500 lives could be saved, and 33,000 hospitalisations avoided during a two-year outbreak if safe and 70% effective Lassa X vaccines were administered to 40% of the population annually, starting within 100 days.

The “100 Days Mission” is a global goal spearheaded by CEPI, to deliver a vaccine against “Disease X” in 100 days, which could prevent an outbreak from spiralling into a pandemic.

The World Health Organisation has identified Lassa fever as one of the pathogens most likely to cause severe future outbreaks.

Climate change, along with other environmental and demographic factors, could put up to 700 million people at risk of developing Lassa fever, underscoring the virus’s pandemic potential and the urgent need for effective vaccines.

Lassa fever symptoms include fever, headache, muscle pain, and vomiting. In severe cases, victims may suffer facial swelling and bleeding from the mouth, nose, vagina, or gastrointestinal tract. Approximately a quarter of those who survive severe Lassa fever infection develop deafness.

This new study estimates that there are, on average, 23,700 hospitalisations and 3,900 deaths per year due to Lassa fever in West Africa. However, the true burden of Lassa fever could be much higher than reported due to limited access to diagnostics and healthcare.

The modelling showed that the most effective vaccination strategy would be a population-wide preventative campaign targeting areas where the virus is endemic. Reactive vaccination programmes in response to local outbreaks averted only one-tenth of the health-economic burden when compared with population-wide preventative campaigns.

Smith said, “To our knowledge, this is the first study to estimate the burden of disease for Lassa fever and to project the impacts of Lassa vaccination campaigns on population health and economies. One major potential benefit of current investment in Lassa vaccine development is increased readiness to rapidly develop and deploy vaccines against future Lassa variants with pandemic potential.”

The researchers concluded, “Our analysis suggests that vaccination campaigns targeting known Lassa fever hotspots will help to alleviate the large health-economic burden caused by this disease. However, expanding vaccination beyond WHO-classified ‘endemic’ districts will be necessary to prevent the large burden of disease estimated to occur in neighbouring areas not currently classified as endemic.”

Improved surveillance is greatly needed to better characterise the epidemiology of Lassa fever across West Africa, which will help inform the design of vaccination campaigns to maximise population health by better targeting those at greatest risk of infection and severe outcomes.

Richard Hatchett, Chief Executive Officer of the Coalition for Epidemic Preparedness Innovations (CEPI), said, “Lassa fever is a serious public health problem in West Africa and is already threatening to spread to other regions as climate and environmental change increase epidemic risk.”

The World Health Organisation remains committed to working with member states, CEPI, and all stakeholders to fast-track the development of a vaccine and other tools necessary to control the spread of Lassa fever and protect communities. “The time is now for concrete actions,” Hatchett emphasised.

Dr Virgil Lokossou, Head of Division – Preparedness and Response at the West African Health Organisation, said, “Lassa fever continues to pose a serious public health threat in West Africa, severely impacting lives, health, and economic systems. This modelling study highlights the burden of Lassa fever and its significant socioeconomic consequences, underscoring the urgent need to accelerate vaccine research and development as part of regional preparedness and response efforts.”

Joanne Turner, Research Associate at the University of Liverpool and joint first author, said, “The Lassa vaccination campaigns included in our analysis were designed to reflect realistic assumptions about vaccine stockpile and administration. Consequently, the impacts of our simulated Lassa vaccination campaigns were modest in countries other than Nigeria, Guinea, Liberia, and Sierra Leone. Yet, the data underlying our model suggest that there is likely already a significant burden of Lassa fever outside these countries.”

Professor Déirdre Hollingsworth of the University of Oxford’s Big Data Institute added, “Lassa fever predominantly affects low-income populations in rural areas and is likely to be highly underreported due to poor healthcare access in these areas. This analysis highlights the potential impact of a vaccine on these populations.”

CEPI is one of the world’s leading funders of Lassa vaccine research and development, investing in six potential vaccine candidates, four of which have progressed into human trials. One of CEPI’s partners, IAVI, has launched the first-ever Phase II clinical trial of a Lassa vaccine in Abuja, Nigeria.

In collaboration with investigators in Nigeria, Benin, Guinea, Liberia, and Sierra Leone, CEPI is also conducting the largest-ever multi-country investigation of Lassa fever epidemiology to improve knowledge about the virus and how to combat it.