Humoral and cellular immune responses in sheep following administration of different doses of an inactivated phase I vaccine against Coxiella burnetii

An inactivated Coxiella burnetii Phase I (PhI) vaccine (Coxevac) is licensed in several European countries for goats and cattle to prevent coxiellosis. The vaccine is also applied to sheep, although detailed information about the ovine immune response and vaccine dose is missing. Eighteen gimmers from a C. burnetii unsuspected flock were randomly divided into three groups of six. Group 1 (Cox1) and 2 (Cox2) were
vaccinated twice with 1 ml and 2 ml Coxevac, respectively, three weeks apart (primary vaccination). The same procedure was applied with Cox3 (2 ml sodium chloride, control group). A third injection (booster) was performed after nine months. Potential side effects were determined by measuring the rectal body temperature and skin thickness at the injection site. Blood samples were collected to detect phasespecific
IgM and IgG antibodies and interferon-ɣ (IFN-ɣ) release by immunofluorescence assay and ELISAs, respectively. Moreover, a cell infection neutralization assay determined the  appearance of neutralizing sera. Body temperatures increased for one day post vaccination, and the skin swelled only slightly. Regardless of the vaccine volume, immunized sheep reacted first with an IgM and IgG PhII response. Ten weeks after the primary vaccination, IgG PhI antibodies predominated. Boosting eight months after primary vaccination resulted in a robust IgG PhI increase and strong IFN-ɣ response. In
the vaccinated animals, the neutralizing effect is more widespread after the administration of 1 ml than after the treatment with 2 ml. In summary, differences between 1 and 2 ml Coxevac are minor, and a vaccine volume of 1 ml seems to be sufficient. A booster after the primary vaccination is apparently necessary
to stimulate the cell-mediated immune response in naïve sheep.