Efficacy of commercially available vaccines against canine leptospirosis: A systematic review and meta-analysis.

BACKGROUND:Leptospirosis is a worldwide distributed zoonosis that affects most mammal species, including dogs and humans. Vaccination is the main strategy to control disease and urinary shedding of leptospires in dogs; however, there are few studies in the literature reporting the efficacy of commercially available vaccines. OBJECTIVES:To access and compare the efficacy of commercially available leptospiral vaccines dogs using a quali-quantitative systematic review. METHODS:The main outcome of interest was the ability to protect dogs against clinical disease and renal carrier state, as well as promoting duration of immunity. Experimental and observational study designs were eligible for inclusion, and methodology was validated by PROSPERO, under registration CRD42020178194. Five electronic databases were searched. Data about population, methodology and outcomes were extracted in a dichotomous or continuous manner. Evaluation of risk of bias for individual studies was assessed using SYRCLE tool. RESULTS:Thirteen challenge trials and eight observational studies were included, comprising 12 vaccine brands. In the calculated pooled effect, vaccinated dogs had a reduced Relative Risk of developing clinical disease (0.16) and renal carrier state (0.12) when compared to unvaccinated controls. The heterogeneity between studies was low; however, methodologies and different parameters were used in the studies to define the outcomes. CONCLUSIONS AND CLINICAL IMPORTANCE:Our study has demonstrated that commercially available vaccines against leptospirosis can provide an overall 84% protection against clinical disease and 88% against renal carrier status. Protection against clinical disease and carrier status by serovars Canicola, Australis and Grippotyphosa is inconsistent for some vaccine brands, and such hurdle is mostly attributed to methodological difficulties in inducing experimental infection using these serovars. Evidence shows that immunity provided by the vaccines included in our meta-analysis can persist for at least one year under experimental conditions. However, the duration of MAT titers induced by vaccination do not correlate with protection.