Inactivated Schmallenberg virus prototype vaccines

Schmallenberg virus (SBV), a novel Orthobunyavirus, is an insect-transmitted pathogen and was first described in Europe in 2011. SBV causes a mild transient disease in adult ruminants, but severe foetal malformation and stillbirth were observed after an infection of naive cows and ewes, which is responsible for considerable economic losses. The virus is now widely distributed in Europe, and no vaccines were available to stop transmission and spread. In the present study, 16 calves and 25 sheep, the major target species of SBV infection, were vaccinated twice 3 weeks apart with one of 5 newly developed, inactivated vaccine candidates. Six calves and 5 sheep were kept as unvaccinated controls. All animals were clinically, serologically and virologically examined before and after challenge infection. Immunisation with the inactivated preparations resulted in a neutralising antibody response three weeks after the second vaccination without any side effects. The number of animals that seroconverted in each group and the strength of the antibody response were dependent on the cell line used for virus growth and on the viral titre prior to inactivation. Four vaccine prototypes completely prevented RNAemia after challenge infection, a fifth candidate reduced RNAemia considerably. Although further evaluations e.g. regarding duration of immunity will be necessary, the newly developed vaccines are promising candidates for the prevention of SBV-infection and could be a valuable tool in SBV control strategies.