What is the potential role of veterinary vaccination in the control of Rift Valley fever in Kenya?

Thesis

Rift Valley fever virus (RVFV) is a zoonotic arbovirus that causes fever, high mortality in young and spontaneous abortions in livestock species. It can have a dramatic impact on livestock health and production as well as on public health and people’s livelihoods. The licensed veterinary vaccines have multiple issues including residual virulence, which underlies their contraindication for use in pregnant animals, the need for high containment facilities for their manufacture and diagnostic tests are unable to differentiate between infected and vaccinated animals (DIVA).

The literature indicated that RVF seroprevalence across the African continent was significantly higher in small ruminants during outbreaks than interepidemic periods (IEPs), suggesting these populations are often naïve when an outbreak occurs. The serosurvey conducted in three Kenyan counties found that RVF seroprevalence was recorded in at-risk areas during IEPs, suggesting silent circulation.

A non-inferiority trial was conducted comparing a promising candidate vaccine, ChAdOx1 RVF, with the commercialised Smithburn vaccine in multiple target livestock species (n=613) under natural environment conditions. The successful conduct of the trial in accordance with veterinary GCP has been underpinned by engagement and collaborations with regulatory authorities and trial monitoring teams across multiple sites in Kenya and abroad. The primary endpoint for the trial was to assess non-inferiority of the ChAdOx1 RVF vaccine compared to the Smithburn vaccine with regards to seroconversion as measured by an RVF virus neutralising antibody assay (FRNT). These seroconversion results were utilised in the development of a transmission dynamics model.

The ChAdOx1 RVF vaccine was found to be safe, DIVA compliant and non-inferior in all species. Vaccine scenarios suggested vaccinating with ChAdOx1 RVF in the dry season annually or every 3 years would decrease cumulative incidence of infected livestock significantly. These results show ChAdOx1 RVF is a promising candidate for registration and use in livestock in areas of risk for RVF.

Authors: Clark, MHA

• DOI: 10.5287/ora-e2mewy8qv
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: OneHealth; Vaccinology; Epidemiology