Monograph 0249 of the European Pharmacopoeia prescribes batch safety testing of inactivated equine virus vaccines. Unexpected fever occasionally occurs with these tests. The purpose of this study was to investigate whether this response is related to components of the inactivated virus or if it is caused by the adjuvant. Ten immune naive foals were randomly allocated to Group A and Group B. The horses of Group A (n= 5) were intramuscularly injected with an inactivated influenzatetanus vaccine (Duvaxyn®IE-T). The horses of Group B (n= 5) received a sham vaccine containing the carbomer and aluminiumhydroxyd adjuvant. Horses received their second injection after 4 weeks. Rectal temperatures were measured daily during the tests (28 days). Blood samples were taken from the horses at 0, 4, 12 hours post first and second vaccination and additionally at 240 hours after the second injection. The protein bands were analysed by SDS-PAGE methods. The fluctuation of the proteins bands was moderate over the time course. The relative mRNA expression of cytokines was measured in peripheral blood mononuclear cells (PBMCs), using the quantitative TaqMan®Real-Time RT-PCR (qRT-PCR) technique. Target gene expression was normalized to total cell amounts. In contrast to what was expected, Group B horses did not show a clear fever response after first and second injection with adjuvant, whereas the mean temperature in Group A was significantly higher at 24 hours p.v.. Relative TNF-alpha expression in PWBC was elevated at all time points in this group, and had returned to basal levels 240 hours after the second injection. IL-4 expression was low in most horses after the first injection and tended to become moderately up-regulated in group A 4 hours after injection. After second injection IL-4 expression was moderately elevated in Group A at all time points.
At 12 hours p.v., horses of group A showed about 100-fold higher induced IL-2 expression levels than horses of group B. In conclusion, the adjuvant does not cause fever, but the fever response seen during vaccine testing might be caused by the antigens of equine influenza virus or the tetanus toxoid. Cytokine expression after vaccination was clearly elevated in PWBC. The mRNA-Expression of TNF-alpha seems to be induced more strongly after the second vaccination in than after the first one. In order to be meaningful as safety guideline, this study indicates that Monograph 0249 of the European Pharmacopoeia should be reworded such that it includes a statement what could be considered as acceptable normal biological post vaccinal reaction.