The experimental vaccine is being developed by researchers at the University of Oxford, a UK-based research institution, with support from the Coalition for Epidemic Preparedness Innovations (CEPI).
A candidate vaccine for Lassa fever has entered its first human trials in the United Kingdom, raising hopes for improved prevention of a disease that continues to cause recurrent outbreaks annually in Nigeria and across West Africa.
The development was disclosed during an interview with PREMIUM TIMES involving global health officials and researchers leading Lassa fever vaccine development.
The experimental vaccine is being developed by researchers at the University of Oxford, a UK-based research institution, with support from the Coalition for Epidemic Preparedness Innovations (CEPI), a global health organisation that funds vaccine development for epidemic-prone diseases.
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The ongoing trial is a Phase one study designed to assess the vaccine's safety in healthy adult volunteers. If successful, the candidate will advance to larger trials in Africa, including Nigeria, one of the countries most affected by the disease.
Long-standing public health threat
Lassa fever is a viral haemorrhagic illness endemic to parts of West Africa. Nigeria records the highest number of reported cases globally each year, with outbreaks often placing a significant strain on the country's public health system.
Despite being identified more than five decades ago, the disease has remained without a licensed vaccine.
Katrin Ramsauer, Lassa programme lead at CEPI, said vaccine development lagged largely because Lassa fever predominantly affects low- and middle-income countries, offering little commercial incentive for pharmaceutical companies.
"Lassa fever has been around since 1969, and survivors often suffer long-term complications such as hearing loss and neurological problems," Ms Ramsauer said, adding that the true disease burden is likely higher than reported.
Ms Ramsauer said CEPI was established after the 2014-2016 Ebola outbreak to address this gap by funding vaccines for epidemic-prone diseases with high public health impact but limited market appeal.
Why early trials begin outside Nigeria
Responding to questions about why Nigeria did not host the initial human trials, Ms Ramsauer said early-stage clinical trials are typically conducted in locations with long-established research infrastructure to ensure safety and speed.
She stressed that Nigeria is already hosting other Lassa fever vaccine studies, including a CEPI-supported Phase two trial by another developer, and remains central to plans.
"Nigeria is absolutely ready for clinical trials," she said, noting that CEPI has invested in strengthening clinical trial capacity in the country to support vaccine research.
Ms Ramsauer added that while the Oxford-led candidate began Phase one trials in the UK, it is expected to move to Ghana for additional early-stage testing before progressing to later phases in Nigeria and other West African countries.
Community trust, vaccine acceptance
Oyeronke Oyebanji, who leads CEPI's Lassa fever engagement in West Africa, said the organisation has been working closely with governments in the region to ensure community acceptance and equitable access to any future vaccine.
She said CEPI, in partnership with the West African Health Organisation, established the Lassa Fever Coalition, which includes Nigeria, Liberia, Sierra Leone, Guinea and the Benin Republic.
According to her, the coalition provides a platform for governments, scientists and policymakers to jointly plan vaccine development, future introduction, pricing and availability.
Ms Oyebanji said CEPI is also funding social science studies in Nigeria, Liberia and Sierra Leone to better understand vaccine hesitancy, willingness to participate in clinical trials and community perceptions around Lassa fever vaccines.
"We are starting early because trust and acceptance are critical, and the context can change over time," she said.
Early trial results
Maheshi Ramasamy, an infectious disease specialist at the University of Oxford, said six healthy volunteers aged between 18 and 50 have so far received the experimental vaccine in the ongoing Phase 1 trial.
Ms Ramasamy explained that the vaccine is built on the ChAdOx1 platform, the same viral vector technology used in the Oxford-AstraZeneca COVID-19 vaccine, which has been administered globally.
She said the platform has an extensive safety record, with billions of doses used worldwide.
According to her, all six participants are doing well, with no serious adverse events recorded.
She said reported side effects have been mild and short-lived, including temporary arm pain, fatigue and headaches, similar to those associated with routine vaccinations.
The trial team is expected to enrol an additional 25 participants in the UK and about 50 in Ghana before advancing to Phase 2 trials, which are expected to include Nigeria.
Preventive tool, not a cure
Ms Ramasamy clarified that the vaccine is designed to prevent Lassa fever, not to treat people already infected with the virus.
She said multiple vaccine candidates are needed to ensure resilience in supply and manufacturing, noting that experiences during the COVID-19 pandemic showed the risks of relying on a single vaccine.
"Having more than one effective vaccine allows us to respond faster and protect different populations during outbreaks," he said.
Lassa fever in Nigeria
Lassa fever is a rodent-borne viral disease that spreads to humans mainly through exposure to food, water or household items contaminated by infected rats, and can also be transmitted between people through contact with bodily fluids.
The illness often begins with non-specific symptoms such as fever and weakness, which can delay care-seeking, but may progress to severe complications including bleeding, respiratory distress and organ failure if not treated early.
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In Nigeria, the disease remains a persistent public health challenge.
As of epidemiological week 51 of 2025, the country recorded 206 deaths from Lassa fever, according to the Nigeria Centre for Disease Control and Prevention (NCDC).
The NCDC said the case fatality rate (CFR) rose to 18.4 per cent, up from 16.4 per cent recorded during the same period in 2024, even though the number of confirmed cases declined during the reporting week.
During the week covering 15-21 December 2025, Nigeria recorded 21 new confirmed cases across seven states, Bauchi, Ondo, Taraba, Edo, Kogi, Ebonyi and Plateau, down from 28 cases the previous week. However, five deaths were recorded among confirmed cases, resulting in a weekly CFR of 23.8 per cent.
Cumulatively, the country reported 1,119 confirmed cases, nine probable cases and 9,270 suspected cases across 21 states and 105 local government areas in 2025.
While this represents a decline in cases compared with 2024, when 1,237 confirmed cases and 203 deaths were reported, the NCDC said fatalities increased largely due to late presentation at health facilities.
Ondo, Bauchi, Edo and Taraba accounted for 88 per cent of confirmed cases in 2025, with Ondo alone contributing 35 per cent.
The NCDC identified late health-seeking behaviour, high treatment costs, poor environmental sanitation and low awareness in high-burden communities as major contributors to the rising fatality rate.
