What is it about?

Rift Valley fever virus (RVFV) is a globally important virus affecting both humans and livestock that is transmitted by vectors and via aerosolization. It causes frequent outbreaks across Africa and several Indian Ocean islands, leading to mass mortality of young livestock and to pregnancy losses among both humans and animals. Not all cases are recognized, especially in adult animals, but severe cases can result in hemorrhagic fever, encephalitis, and death in humans. There is currently no human vaccine option, but several candidates are under development. The goal of our systematic review was to consolidate recent RVFV epidemiology to identify key knowledge gaps relevant to planning human vaccine trials. We retrieved primary RVFV data from an extensive variety of sources and identified that, globally, over the past two decades, human outbreaks have occurred at a rate of 5.8 per year and animal outbreaks at 12.4 per year. Mauritania, Madagascar, Kenya, South Africa, and Sudan had the most human outbreak years, and risk of human infection was associated with animal contact, butchering, milking, and handling of aborted materials. RVFV circulation was also detected in multiple different local mosquito species even outside of recognized outbreak periods.

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Why is it important?

Alongside current RVFV control measures, the implementation of anti-RVFV human vaccination has strong potential to limit the future impact of this now widely-endemic hemorrhagic fever virus. In our study, we highlighted potential gaps that could affect successful planning and implementation of future trials to test new anti-RVFV human vaccines. These knowledge gaps included the changing interval between outbreaks, challenges of variable pre-existing livestock immunity, a mixed understanding of human risk factors, inconsistent frameworks for diagnostic testing, and the need to harmonize coordinated One Health human-animal control approaches. Proper integration of these factors will help to optimize vaccine trial design.


Rift Valley fever virus has the potential to become the next global pandemic. The time to blunt this threat is now, and creation of a safe and effective vaccine for humans will be one key to control.

Charles King
Case Western Reserve University

Read the Original

This page is a summary of: Paving the way for human vaccination against Rift Valley fever virus: A systematic literature review of RVFV epidemiology from 1999 to 2021, PLoS Neglected Tropical Diseases, January 2022, PLOS, DOI: 10.1371/journal.pntd.0009852.
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