New vaccine against Rift Valley fever is safe and effective in pregnant sheep

A study by Wageningen Bioveterinary Research (WBVR), in collaboration with BunyaVax and Ceva Animal Health, shows that a new live-attenuated candidate vaccine against Rift Valley fever virus (RVFV) is safe and effective in pregnant sheep. Previously developed live-attenuated vaccines protect the ewe, but proved to be harmful to the foetus.

RVFV is a virus that is transmitted by mosquitoes to ruminants and humans. Sheep are particularly susceptible to the virus. The consequences of a RVFV infection are particularly serious in newborn lambs, most of which will not survive the infection. An RVFV infection of pregnant sheep will result in abortion. Infections of humans generally result in flu-like symptoms, with a small percentage developing serious and potentially fatal disease. At present, the virus is only found on the African continent and on the Arabian peninsula. The mosquitoes that can transmit the virus are found the world over, including in the Netherlands. Globalisation, climate change and increasing animal and human populations increase the risk of future RVF outbreaks worldwide.

An attenuated RVF virus as a vaccine

Conventional RVF vaccines are based on either inactivated- or live-attenuated virus. Inactivated RVF vaccines are safe for animals during all physiological stages, including pregnancy. Optimal efficacy of these vaccines, however, depends on multiple vaccinations and annual re-vaccination. Live-attenuated vaccines are generally very effective after a single vaccination, but the live-attenuated vaccines against RVF that are currently available can be transmitted to the foetus, which may lead to stillbirth, congenital abnormalities and abortion. In contrast to these conventional vaccines, the new RVF vaccine proved to be entirely safe for pregnant animals, even after administration of a very high dose. The current study shows that the live-attenuated vaccine provides complete protection following a single vaccination.

RVF vaccine for humans

The technology that has been used to develop the vaccine for animals is also applied for the development of an RVF vaccine that can be used in humans. This candidate vaccine is currently being developed as part of the LARISSA project, which is financed by the Coalition for Epidemic Preparedness Innovations. The safety of this vaccine will be evaluated in a first-in-human clinical trial initiating in 2021.

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