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Developing Rift Valley fever vaccines that optimally combine efficacy and safety

BunyaVax proprietary vaccine technology

BunyaVax develops novel vaccine platform technologies for generating safe and efficacious vaccines against neglected tropical diseases, with a focus on diseases that threaten public and veterinary health in developing countries. The current focus of the company is on Rift Valley fever virus (RVFV), a mosquito-transmitted pathogen of ruminants and humans that can affect millions of animals and thousands of humans in single outbreaks. BunyaVax is leading the LARISSA project ( that is funded and supported by the Coalition for Epidemic Preparedness Innovations (CEPI:, which aims to develop a human Rift Valley fever vaccine. In parallel, BunyaVax is developing a vaccine for veterinary use in collaboration with a world-leading animal health company. More information about RVFV and the technology used to develop human and veterinary vaccines is given below. 

Rift Valley fever virus 

Rift Valley fever virus (RVFV) is a mosquito-borne bunyavirus. The virus contains an RNA genome that is divided into three segments, named after their size. The large (L) segment encodes the viral polymerase, the medium (M) segment encodes the two structural glycoproteins Gn and Gc that are involved in binding to the target cell and fusion of the viral and endosomal membranes, respectively. The small (S) segment encodes the nucleocapsid (N) protein and a nonstructural protein named NSs. The NSs protein is the major virulence determinant of RVFV by counteracting host innate immune responses. Using reverse-genetics (genetic modification), the NSs protein can be deleted from the RVFV genome, resulting in a virus that is highly attenuated. RVFV strains lacking NSs have been evaluated as vaccines. Whereas these attenuated viruses are safe for non-pregnant animals, vertical transmission of these viruses may result in congenital malformations and stillbirths. The BunyaVax 4s technology is based on an additional method of attenuation in which the M genome segment is split into two M-type genome segments. This results in a four-segmented RVFV, which was shown to be completely safe even in pregnant ewes and to provide complete protection in sheep, goats and cattle.  

BunyaVax proprietary 4s technology

BunyaVax applies its 4s technology to create live-attenuated vaccines against bunyaviruses such as Rift Valley fever virus. Live-attenuated vaccines hold great promise, as these vaccines can be produced cost-effectively and provide long-lasting protection after a single vaccination.

The 4s technology is based on splitting the M genome segment of the virus into two separate segments. This resulted in a four-segmented RVFV (RVFV-4s). RVFV-4s was shown to be completely avirulent in mice, sheep, goats, cattle and nonhuman primates. To optimize vaccine safety, the NSs protein, which is the major virulence factor of the virus, was removed from the genome. 

Excellent efficacy and safety of 4s vaccines was demonstrated by:

  • Induction of sterile immunity after a single vaccination of lambs, goats and cattle. 

  • Absence of clinical signs after administration of an overdose to young lambs and pregnant ewes. 

  • Absence of viremia after administration of an overdose

  • Absence of dissemination, shedding and spreading after administration of an overdose

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Virus neutralization test of unmatched sensitivity and specificity

Apart from vaccine development, the 4s technology was also used to develop a virus neutralization test (VNT) that is of unmatched sensitivity and specificity. The VNT test is considered the gold standard test to diagnose RVFV infection, due to its higher sensitivity and specificity compared to ELISA. Classical VNTs make use of attenuated RVFV strains. However, as none of these strains are completely avirulent, these assays have to be performed in BSL-2 or even BSL-3 laboratories. This severely complicates diagnostic performance, especially in developing countries. BunyaVax has developed a novel VNT that makes use of a RVFV-4s virus expressing green fluorescent protein (GFP). The RVFV-4s VNT was shown to be of even higher sensitivity as classical VNTs. The VNT is described in Wichgers Schreur et al., J Virol Methods. 2017;248:26-30. 

Published results

Creation of a nonspreading Rift Valley fever virus. Kortekaas J, Oreshkova N, Cobos-Jiménez V, Vloet RP, Potgieter CA, Moormann RJM. J Virol. 2011 Dec;85(23):12622-30.


Efficacy of three candidate Rift Valley fever vaccines in sheep. Kortekaas J, Antonis AF, Kant J, Vloet RP, Vogel A, Oreshkova N, de Boer SM, Bosch BJ, Moormann RJM. Vaccine. 2012  30:3423-3429.


A single vaccination with an improved nonspreading Rift Valley fever virus vaccine provides sterile immunity in lambs. Oreshkova N, van Keulen L, Kant J, Moormann RJ, Kortekaas J. PLoS One. 2013 Oct 22;8(10):e77461.


Creation of Rift Valley fever viruses with four-segmented genomes reveals flexibility in bunyavirus genome packaging. Wichgers Schreur PJ, Oreshkova N, Moormann RJ, Kortekaas J. J Virol. 2014;88(18):10883-93.


Comparative efficacy of two next-generation Rift Valley fever vaccines. Kortekaas J, Oreshkova N, van Keulen L, Kant J, Bosch BJ, Bouloy M, Moulin V, Goovaerts D, Moormann RJ. Vaccine. 2014 Sep 3;32(39):4901-8.


Evaluation of nonspreading Rift Valley fever virus as a vaccine vector using influenza virus hemagglutinin as a model antigen. Oreshkova N, Cornelissen LA, de Haan CA, Moormann RJ, Kortekaas J. Vaccine. 2014;32(41):5323-9.


Four-segmented Rift Valley fever virus induces sterile immunity in sheep after a single vaccination. Wichgers Schreur PJ, Kant J, van Keulen L, Moormann RJ, Kortekaas J. Vaccine. 2015 Mar 17;33(12):1459-64.


Preliminary Evaluation of a Bunyavirus Vector for Cancer Immunotherapy. Oreshkova N, Spel L, Vloet RP, Schreur PJ, Moormann RJ, Boes M, Kortekaas J. J Virol. 2015 Jun 17. pii: JVI.01105-15.


Four-segmented Rift Valley fever virus-based vaccines can be applied safely in ewes during pregnancy. Wichgers Schreur PJ, van Keulen L, Kant J, Kortekaas J. Vaccine. 2017;35:3123-3128.

A novel highly sensitive, rapid and safe Rift Valley fever virus neutralization test. Wichgers Schreur PJ, Paweska JT, Kant J, Kortekaas J. J Virol Methods. 2017 Oct;248:26-30.

Safety and efficacy of four-segmented Rift Valley fever virus in young sheep, goats and cattle. Wichgers Schreur PJ, Oreshkova N, van Keulen L, Kant J, van de Water S, Soós P, Dehon Y, Kollár A, Pénzes Z, Kortekaas J. NPJ Vaccines. 2020 Jul 24;5:65. doi: 10.1038/s41541-020-00212-4. eCollection 2020.

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