Promising human Rift Valley fever vaccine to enter Phase II clinical trials in Kenya

• New CEPI-funded trial to launch in Kenya – the first ever Phase II trial of a Rift Valley fever vaccine in an endemic country
• Earlier vaccine studies show positive safety data, and generation of an immune response 
• Rift Valley fever is a mosquito-borne disease affecting people and animals across Africa 

October 13, OSLO, Norway, and NAIROBI, Kenya - – A promising human vaccine candidate against the potentially deadly Rift Valley fever, a mosquito-borne disease affecting countries across Africa, is set to begin Phase II trials in Kenya. This is the most advanced stage of testing a human Rift Valley fever vaccine has reached in an outbreak-prone area to date.

A team of scientists at the University of Oxford and the Kenya Medical Research Institute (KEMRI)-Wellcome Trust Research Programme will lead the $3.7m trial, funded by CEPI. A total of 240 healthy adult participants will take part in the research, following local trial approvals. Participants will be closely monitored, assessing the safety and ability of the vaccine candidate to elicit an immune response against Rift Valley fever. The vaccine has been developed on the University of Oxford’s ChAdOx1 vaccine platform, the same technology behind the Oxford-AstraZeneca COVID-19 vaccine which has saved millions of lives worldwide. 

Welcoming the new trial, Professor George Warimwe, Principal Investigator of the upcoming trial and Deputy Executive Director of the KEMRI-Wellcome Trust Research programme, said: “Nearly 100 years after Rift Valley fever was discovered, there are still no approved vaccines or treatments against the disease. This vaccine trial brings us closer to addressing the rising frequency of outbreaks.”

Rift Valley fever usually occurs in people following direct contact with infected animals, like sheep, goats and cattle, or bites from infected mosquitoes. While the majority of people infected experience mild disease, a small proportion develop the severe haemorrhagic form, which can cause blindness, convulsions, encephalitis and bleeding, and mortality rates of up to 50%. 

Rift Valley fever was first identified in Kenya's Rift Valley, but in recent decades has been detected across much of Africa and also in the Middle East. As a mosquito-borne, and therefore climate-sensitive infectious disease, there is a risk of Rift Valley fever outbreaks spreading to new areas or increasing in frequency or size as a result of extreme or unusual weather events. 

While Rift Valley fever vaccines have been registered for animals, no vaccines are currently available or licensed for human use. Both the World Health Organization and Africa Centres for Disease Control and Prevention have identified Rift Valley fever as a priority disease for R&D.

The promising Rift Valley fever vaccine candidate to be evaluated in people in Kenya is known as ChAdOx1 RVF. It has already shown positive results in the first stage of clinical trials conducted in the UK. The trial demonstrated that the vaccine was safe and well-tolerated in volunteers who received a single shot of the vaccine, and that it elicited high levels of neutralising antibodies which block viral infection and mediate protection against the virus. Of three dosing levels assessed, these immune responses were highest in the medium-dose and high-dose vaccines. Studies have also shown that the vaccine provides protection against Rift Valley fever in multiple livestock species, suggesting that it could potentially be used for both people and livestock.

ChAdOx1 RVF becomes one of three Rift Valley fever vaccine candidates in CEPI’s portfolio. 

“Rift Valley fever disproportionately affects the lives and livelihoods of vulnerable pastoral communities, potentially causing both human fatalities and large-scale livestock losses” said Dr Richard Hatchett, CEO of the Coalition for Epidemic Preparedness Innovations. “Investing in the promising human ChAdOx1 RVF vaccine diversifies CEPI’s portfolio and gives us a greater chance at protecting vulnerable populations against this worrisome threat that may become more prevalent with climate change.”

H.E. Dr. Jean Kaseya, Director General of Africa CDC, said: “Rift Valley fever (RVF) is a zoonotic disease that leads to livestock losses and human fatalities, thus impoverishing communities who largely depend on livestock for their livelihood. The launch of a Phase II clinical trial of a Rift Valley fever vaccine candidate in an endemic country is a crucial milestone in our efforts to control this disease. Africa CDC is proud to support this initiative that not only prioritize the health of our people but also demonstrate the continent’s growing leadership in advancing clinical research. The ChAdOx1 RVF vaccine offers hope to vulnerable populations who are disproportionately affected by the growing impact of climate change.”

Funding for the new trial is awarded under CEPI’s strategic partnership with the University of Oxford - a broad collaboration which seeks to accelerate the development of globally accessible vaccines against outbreak pathogens.

CEPI and the University of Oxford are committed to enabling access to any vaccine outputs developed through this partnership, in line with CEPI’s Equitable Access Policy. This includes developing a target product profile suitable for low- and middle-income countries, assessing the need for technology transfer to low- and middle-income countries, and priority supply to low- and middle-income countries at an affordable price, with a public health license which grants CEPI a non-exclusive, worldwide, royalty free license to develop the vaccine and achieve equitable access, should the vaccine candidate be shown to be safe and effective in clinical testing. The clinical trial data generated by this project will be published open access to benefit public health and research communities.

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Notes to Editors

Rift Valley fever is a mosquito-borne viral illness of humans and farm animals that was first discovered in Kenya’s Rift Valley in 1930, but in recent decades has been detected in many African countries and parts of the Middle East, putting more people in more countries at risk of infection. 

Because of its impact on both people and animals, Rift Valley fever has profound direct and indirect human health impacts – affecting both lives and livelihoods directly. A ‘One Health’ approach to disease control will work for Rift Valley fever. While vaccines are available for veterinary use, no vaccines are currently available for human use.

Outbreaks of Rift Valley fever have been consistently linked with intense periods of rainfall and flooding including those caused by the El Niño phenomenon which has recently returned after a seven year absence. Heavy rains provide ideal conditions for Rift Valley fever-infected mosquitoes to breed and hatch. As climate change persists, expanding the range of mosquitoes and increasing the likelihood of extreme weather events such as flooding, there is a risk that Rift Valley fever outbreaks will become more frequent and widespread making the development of a protective human vaccine all the more urgent.

About CEPI 

CEPI was launched in 2017 as an innovative partnership between public, private, philanthropic, and civil organisations. Its mission is to accelerate the development of vaccines and other biologic countermeasures against epidemic and pandemic disease threats and enable equitable access to them. CEPI has supported the development of more than 50 vaccine candidates or platform technologies against multiple known high-risk pathogens and is advancing the development of rapid response platforms for vaccines against a future Disease X. Central to CEPI’s pandemic-beating five-year plan for 2022-2026 is the ‘100 Days Mission’ to compress the time taken to develop safe, effective, globally accessible vaccines against new threats to just 100 days.

About the University of Oxford

Oxford University has been placed number 1 in the Times Higher Education World University Rankings for the eighth year running, and number 3 in the QS World Rankings 2025. At the heart of this success are the twin-pillars of our ground-breaking research and innovation and our distinctive educational offer. Oxford is world-famous for research and teaching excellence and home to some of the most talented people from across the globe. Our work helps the lives of millions, solving real-world problems through a huge network of partnerships and collaborations. The breadth and interdisciplinary nature of our research alongside our personalised approach to teaching sparks imaginative and inventive insights and solutions.

About KEMRI-Wellcome Trust Research Programme

The Kenya Medical Research Institute (KEMRI)-Wellcome Trust Research Programme formally established in 1989, is a partnership between KEMRI, Oxford University and the Wellcome Trust. We conduct high quality, purposeful, and relevant research in molecular biology, epidemiological and clinical research. This research feeds directly into local and international health policy, with a parallel aim of supporting and nurturing the next generation of African researchers www.kemri-wellcome.org.