Meta-analysis of the efficacy of Leptospira serovar Hardjo vaccines to prevent urinary shedding in cattle

Leptospirosis is a zoonosis often associated with occupational exposure from livestock that can be prevented by animal vaccination. Several trials have assessed vaccine efficacy in livestock but there have been no attempts to evaluate these trials jointly. This systematic review and meta-analysis aimed to estimate vaccine efficacy to prevent urinary shedding of Leptospira serovar Hardjo (Hardjo) in cattle. Three databases were used to search for relevant papers published from 1980 to 2015 evaluating commercial vaccines to prevent urinary shedding of leptospires after artificial conjunctival or natural challenge. A total of 1237 articles were initially identified. Eight articles containing information from nine trials that assessed vaccine efficacy to prevent Hardjo urinary shedding, as per bacteriological culture, were included in the meta-analysis. Fixed effects Mantel-Haenszel (MH) and a Bayesian random effects meta-analyses were used to estimate the efficacy of vaccination to prevent Hardjo shedding in urine. Vaccine efficacy against Hardjo challenge was 88.7% (95% CI 81.0%-93.2%) in the MH meta-analysis and 89.9% (95% probability interval 80.6%-94.9%) in the Bayesian random effects meta-analysis. There was no evidence of heterogeneity of study results (p = 0.17). The estimated vaccine efficacy to prevent urinary shedding of Hardjo in cattle may be sufficient to reduce disease incidence in animals and exposure risk of people working in close contact with cattle.