A Systematic Review and Meta-Analysis of Phase I Inactivated Vaccines to Reduce Shedding of Coxiella burnetii From Sheep and Goats From Routes of Public Health Importance

Q fever in humans and coxiellosis in livestock are both caused by Coxiella burnetii. The public health importance of vaccination against C.burnetii shedding from sheep and goats was evaluated using systematic review and meta-analysis to provide evidence for policy direction to prevent potential zoonotic spread. Publications reporting shedding of C.burnetii in vaginal and uterine secretions, milk, placenta and faeces were included. A single observational (one goat) and seven experimental (four goat and three sheep) vaccine studies were included in the review. No relevant publications on other interventions were identified. Random effects meta-analyses were performed for the risk of shedding in individuals in the control and vaccinated groups and for the mean difference in the level of bacterial shedding in sheep and goats stratified by age and previous exposure status. Limited data were available for further analytic evaluation. From the pooled analysis, an inactivated phase I vaccine significantly reduced the risk of shedding from uterine (RR=0.10; 95%CI 0.05-0.20) secretions in previously sensitized goats. Individual studies reported significant risk reduction in milk (RR=0.03; 95%CI 0.01-0.26), vaginal secretions (RR=0.40; 95%CI 0.22-0.75) and faeces (RR=0.79; 95%CI 0.63-0.97) from naive goats. The pooled mean levels of bacteria shed from placental [mean difference (MD=-5.24 Log(10); 95%CI -6.75 to -3.7)] and vaginal (MD=-1.78 Log(10); 95%CI -2.19 to -1.38) routes were significantly decreased in vaccinated naive goats compared with controls. Shedding through all other routes from vaccinated goats was not significantly different than shedding from control goats. No effect of vaccination was found on the risk of shedding or the mean level of shedding in vaccinated sheep compared with control sheep. Our conclusions are based on a limited amount of data with variable risk of systematic error.