A systems serology analysis of correlates of protection against cholera

Abstract

AbstractVibriocidal antibodies are the best characterized correlate of protection against cholera and are used to gauge immunogenicity in vaccine trials. However, there is no vibriocidal titer threshold associated with absolute protection against infection with Vibrio cholerae or with symptomatic disease in infected individuals. While other circulating antibody responses have also been associated with a decreased risk of V. cholerae infection, there has been no comprehensive comparison of correlates of protection against cholera. To address this, we analyzed 58 serum antibody biomarkers as correlates of protection against both V. cholerae infection and against cholera diarrhea in infected individuals. The study was performed in two cohorts: (1) household contacts of patients with cholera in Bangladesh, and (2) North American volunteers who were vaccinated with a single dose of CVD 103-HgR live oral cholera vaccine and then challenged with virulent V. cholerae O1 El Tor Inaba. In household contacts, we identified 20 antibody markers that were correlated with protection against V. cholerae infection, though there was overlap between distributions. Conditional random forest models identified serum antibody-dependent complement deposition, targeting the V. cholerae O1 antigen, as the most predictive individual correlate of protection from infection, while vibriocidal antibody titers were less predictive. The model that most accurately predicted protection from infection included five biomarkers, with a cross-validated area under the curve (cvAUC) of 79% (95% CI 73-85). Similarly, in North American volunteers who were challenged with V. cholerae after vaccination, a different five-biomarker model predicted protection from the development of cholera diarrhea with a cvAUC of 78% (95% CI 66-91). Thus, while several new biomarkers predict protection better than vibriocidal titers, it remains difficult to consistently predict whether an individual will be protected from future mucosal infection or symptoms using current serologic markers.