Rift Valley Fever Vaccine Enters Phase II Trials in Kenya Using Oxford's ChAdOx1 Platform
Key Insights
The ChAdOx1 RVF vaccine candidate, developed using the same platform as the Oxford-AstraZeneca COVID-19 vaccine, has begun Phase II clinical trials in Kenya with 240 healthy adult participants.
Phase I trials demonstrated the vaccine was safe and well-tolerated, eliciting high levels of neutralizing antibodies that block viral infection, with medium and high doses showing the strongest immune responses.
This represents the most advanced stage of testing for Rift Valley fever (search) vaccines in an outbreak-affected region, addressing a critical unmet medical need as no vaccines are currently licensed for human use.
A promising Rift Valley fever (search) vaccine candidate has begun Phase II clinical trials in Kenya, marking the most advanced stage of testing for vaccines against this potentially deadly disease in an outbreak-affected region. The ChAdOx1 RVF vaccine, developed using the University of Oxford's ChAdOx1 platform—the same technology behind the life-saving Oxford-AstraZeneca COVID-19 vaccine—started vaccinating volunteers on July 8, 2025, at the KEMRI-Wellcome Trust Research Programme in Kilifi, Kenya.
Trial Design and Participants
The Phase II study will enroll 240 healthy adult participants who will be closely monitored to assess both the safety profile and the vaccine's ability to elicit an immune response against Rift Valley fever (search). This research represents a critical milestone in vaccine development, bringing the scientific community closer to having a licensed Rift Valley fever vaccine available for human use.
Promising Phase I Results
The vaccine candidate has already demonstrated encouraging results in earlier Phase I clinical trials conducted in the UK and Uganda. The initial studies showed that ChAdOx1 RVF was safe and well-tolerated in volunteers who received a single shot of the vaccine. Importantly, the vaccine elicited high levels of neutralizing antibodies that block viral infection and mediate protection against the virus. Of the three dosing levels assessed in Phase I trials, immune responses were highest in the medium-dose and high-dose formulations.
Disease Burden and Clinical Impact
Rift Valley fever (search) typically occurs in people following direct contact with infected animals such as sheep, goats, and cattle, or through bites from infected mosquitoes. While the majority of infected individuals experience mild disease, a small proportion develop the severe hemorrhagic form, which can cause blindness, convulsions, encephalitis, and bleeding, with mortality rates reaching up to 50%.
The disease was first identified in Kenya's Rift Valley but has since been detected across much of Africa and the Middle East in recent decades. As a mosquito-borne and climate-sensitive infectious disease, there is growing concern about the risk of Rift Valley fever (search) outbreaks spreading to new areas or increasing in frequency and severity due to extreme or unusual weather events.
Addressing Critical Unmet Medical Need
Currently, no vaccines are available or licensed for human use against Rift Valley fever (search), despite vaccines being registered for animals. This significant gap in medical countermeasures has led both the World Health Organization and Africa Centres for Disease Control and Prevention to identify Rift Valley fever as a priority disease for research and development.
Professor George Warimwe, Principal Investigator of the upcoming trial and Deputy Executive Director of the KEMRI-Wellcome Trust Research Programme, emphasized the historical significance of this development: "Nearly 100 years after Rift Valley fever (search) 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."
Dual-Use Potential
Studies have demonstrated that the ChAdOx1 RVF vaccine provides protection against Rift Valley fever (search) in multiple livestock species, suggesting it could potentially serve as a dual-use vaccine for both human and animal populations. This characteristic could prove particularly valuable in addressing the disease's impact on vulnerable pastoral communities.
Global Health Security Implications
Dr. Richard Hatchett, CEO of CEPI, highlighted the vaccine's importance for vulnerable populations: "Rift Valley fever (search) disproportionately affects the lives and livelihoods of vulnerable pastoral communities, potentially causing both human fatalities and large-scale livestock losses. 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 (search), emphasized the continental significance of the trial: "The launch of a Phase II clinical trial of a Rift Valley fever (search) 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."
The trial represents part of CEPI's broader strategy to develop vaccines against known threats like Rift Valley fever (search) while building knowledge and systems to prepare for unknown "Disease X" threats, supporting the organization's 100 Days Mission to boost regional health security and enable more rapid responses to emerging health threats.