Lassa: The Race for a Vaccine

Since doctors first identified Lassa fever in 1969, when four missionary nurses died from the viral haemorrhagic illness in the town of Lassa in Borno State, outbreaks have taken place frequently, with 27 states recording at least one confirmed case in 2025. It’s that time of the year again. January through March, when the cold […]

Since doctors first identified Lassa fever in 1969, when four missionary nurses died from the viral haemorrhagic illness in the town of Lassa in Borno State, outbreaks have taken place frequently, with 27 states recording at least one confirmed case in 2025.

It’s that time of the year again. January through March, when the cold harmattan breeze delivers the horrible tidings of Lassa fever.

We are currently facing another Lassa fever outbreak, and like the ones before, lives have been lost and the systemic challenges to optimal treatment and prevention remain the same. The other day, a friend called and asked when she heard the news: ‘Is there no vaccine for Lassa fever yet? Why is it taking so long?’

I simply sighed and continued eating my mango.

Research for a vaccine began in the 70s, but progress has been slow due to a combination of scientific, regulatory, and logistical hurdles. 

Scientists argue that the main reason for the lack of a vaccine is the extensive genetic diversity of the Lassa virus across different geographic regions, with at least seven distinct lineages identified. They argue that a successful vaccine must provide broad protection against all circulating strains, which complicates development and efficacy testing.

But that is just a tiny fraction of the truth. A vaccine has not been developed yet because of the lack of commercial incentive (due to the disease primarily affecting low-income countries) and insufficient political commitment. In other words, international funders cannot be bothered by a poor man’s disease. It is not their priority.

Shikenan. Plain and simple.

Recently, at the University of Oxford, a first volunteer rolled up their sleeve in what researchers described as a cutting-edge clinical trial of a Lassa fever vaccine candidate. For years, Lassa fever has lived in the shadow of more glamorous global health emergencies: Ebola, with its dramatic hemorrhagic headlines, COVID-19, with its planetary paralysis, while Lassa simmered, flared, retreated, and returned, year after year, in Nigeria, Sierra Leone, Liberia, and Guinea.

Today, several vaccine candidates are in preclinical or early-phase clinical trials, supported by international initiatives like the Coalition for Epidemic Preparedness Innovations (CEPI). Promising candidates include viral vector (like the one in an ongoing Phase 2 trial by IAVI and partners) and mRNA-based approaches, which have shown safety and immunogenicity in early trials. 

Across the Atlantic, the International AIDS Vaccine Initiative (IAVI) has been advancing its own candidate, known as IAVI C105, into clinical trials, marking another important step in what is increasingly becoming a multi-front campaign against the virus. Vaccine development, however, is rarely a straight line; it is a long, iterative negotiation between safety, immunogenicity, scalability, and the unpredictable choreography of human biology. In the Phase 1 trial conducted in the United States and Liberia, the candidate was found to be well-tolerated and immunogenic, with robust immune responses that appeared to be sustained for up to one year after vaccination. For scientists, such phrases carry enormous weight because “well tolerated” means no alarming safety signals, and “immunogenic” means the immune system recognized the viral antigens and mounted a measurable defense. Yet even as these early data generate cautious optimism, they do not erase the reality that many promising vaccines have stumbled in later phases, where larger and more diverse populations test the resilience of early findings.

For those of us practicing medicine in Nigeria, especially in regions where Lassa is not an abstract concept but a seasonal dread, the vaccine race feels deeply personal. I have seen the fear in the eyes of healthcare workers after a needle-stick injury from a febrile patient later confirmed to have Lassa. I have witnessed the silent devastation in maternity wards when a pregnant woman with undiagnosed Lassa fever deteriorates rapidly. A vaccine, if proven effective and accessible, would not merely be a biomedical achievement; it would be a moral recalibration of risk for frontline workers and vulnerable families.

But the race is unfolding against a backdrop that is itself shifting. Just as we are rejoicing about the possibility of a vaccine, I read a report on the effect of climate change on Lassa fever. Climate change is no longer a distant environmental debate; it is altering disease ecology in ways that are both subtle and profound.

In many Nigerian communities, environmental changes are already palpable. Deforestation pushes rodents closer to human settlements; flooding displaces families into overcrowded shelters; expanding peri-urban settlements blur the line between bush and bedroom. When we speak of 200 million people potentially at risk, we are not invoking a distant statistical abstraction; we are speaking of farmers storing grain in their homes, market women sleeping near produce, children playing in compounds where rodents forage at night. Climate change does not introduce Lassa to these communities; it amplifies the already existing wahala.

Then again, there is the issue of equitable distribution.

Nigeria, which bears the highest burden of Lassa fever cases annually, must not be a passive recipient at the end of this pipeline. Clinical trials in Liberia and the United States are important, but eventual Phase 2 and Phase 3 trials will need to meaningfully engage endemic populations, not merely as participants but as partners. Community engagement is not a public relations afterthought; it is the difference between vaccine acceptance and vaccine hesitancy.

We have learned, sometimes painfully, that scientific breakthroughs do not automatically translate into public health victories. The story of the HPV vaccine rollout in northern Nigeria, which I have been privileged to work on, reminds us that evidence must be accompanied by advocacy, cultural sensitivity, and sustained investment. A Lassa vaccine, if approved, will require cold chain systems, training of health workers, integration into routine immunization schedules or targeted campaigns, and above all, trust.

For now, the data suggest that the leading candidate is on the right track, but the road ahead remains long and exacting. Larger trials will test the durability of protection, optimal dosing schedules, and efficacy in populations with varying nutritional status and co-morbidities. Regulators will scrutinize safety signals with understandable rigor. Funders will weigh competing global health priorities. And climate change will continue to redraw the epidemiological map in the background.

If the projections are correct and hundreds of millions more people could find themselves within the ecological reach of the Lassa virus, then the urgency of this vaccine race cannot be overstated. What is being tested in Oxford and in IAVI-supported sites is not merely a candidate vaccine; it is our collective capacity to anticipate and invest before we are hit by another catastrophe.

May the best man win. And may a safe vaccine be made available.