Correlates of Protection for Cholera

Area of Science:

• Immunology
• Vaccinology
• Microbiology

Background:

• A correlate of protection (CoP) measures immune response linked to protection from disease after vaccination or infection.
• The reliability of a CoP as a surrogate for vaccine efficacy hinges on the strength of its association with protection.
• For cholera, antitoxin responses to Vibrio cholerae are not linked to long-term immunity and are poor CoPs.

Purpose of the Study:

• To evaluate the suitability of correlates of protection (CoPs) for cholera vaccines.
• To determine if existing measures accurately reflect protective immunity against Vibrio cholerae.
• To assess the association between vibriocidal antibody titers and long-term cholera immunity.

Main Methods:

• Review of existing literature on cholera immunity and vaccine correlates.
• Analysis of the association between different immune responses (antitoxin, anti-O-polysaccharide, vibriocidal antibodies) and protection against Vibrio cholerae.
• Evaluation of vibriocidal antibodies as surrogate endpoints for cholera vaccine efficacy.

Main Results:

• Functional antibodies targeting the O-polysaccharide outer membrane of Vibrio cholerae, not antitoxin responses, appear crucial for protection.
• Vibriocidal antibodies are the most accepted CoP for cholera and are used as surrogate endpoints in some vaccine studies.
• The association between vibriocidal antibody titers and immunity is not absolute, suggesting they may not fully represent a mechanistic correlate of protection.

Conclusions:

• Protection against cholera is likely mediated by antibodies targeting the Vibrio cholerae O-polysaccharide.
• Vibriocidal antibodies, while accepted, may not be a perfect surrogate for cholera vaccine efficacy due to limitations in their association with immunity.
• Further research is needed to identify more robust mechanistic correlates of protection for cholera vaccines.