Vaccine- and Infection-derived Correlates of Protection for Cholera

Vaccine- and Infection-derived Correlates of Protection for Cholera

Background: Vibrio cholerae causes millions of cholera cases and thousands of deaths annually. Vaccines are in short supply. There is no agreement on how to introduce new vaccines or evaluate their effectiveness, and the lack of 'correlates of protection' (CoPs) against cholera is a major obstacle to vaccine development. CoPs are markers of effective immune response to vaccination. While other infectious diseases have well established CoPs, none are widely accepted for cholera.

Relevance: Lack of accepted CoPs impedes development of cholera vaccines, limiting progress toward improved vaccines, slowing the licensure of new vaccines, and contributing to the current vaccine shortage; an immediate obstacle to achieving reductions in cholera-related illness and deaths. The identification of new CoPs will speed the development of improved cholera vaccines and provide a pathway to their licensure and use.

Hypothesis: The investigators hypothesize that some individuals who receive inactivated oral cholera vaccine (OCV) will develop antibody responses which predict protection against V. cholerae infection and that specific immune responses distinguish individuals who are protected against cholera by prior natural infection from those who are protected from OCVs.

Objectives: The investigators will administer an OCV or typhoid vaccine (TCV) control and monitor antibody responses to identify better CoPs for cholera following both vaccination and natural infection.

Methods: The investigators will randomize 1219 participants; 554 participants will receive an inactivated bivalent OCV, 665 participants will receive a TCV control. The investigators will collect 12 blood samples over two-years following vaccination to measure antibodies against V. cholerae and to monitor for re-infection.

Outcome measures/variables: The endpoint of interest is V. cholerae infection after vaccination. The investigators define infection as positive culture or PCR for V. cholerae or seroconversion events observed over the 2-year follow up period.

Inclusion criteria

1. Ages 2 - 80 years.
2. Informed consent from study participants and guardian in case of children (2-17 years) and assent from children aged 11-17 years.
3. Intention to participate in the study for a 2-year period.
4. No major co-morbid conditions, per the supervising clinician investigator, including underlying immunodeficiency, diabetes, liver diseases, renal disease, cardiac disease, and/or active malignancy.

Exclusion criteria

1. Suffering from diarrhoea or abdominal pain or vomiting in the past 24 hours or diarrhoea lasting for more than 2 weeks in the past 6 months.
2. History of taking another oral cholera vaccine.
3. History of taking any other live or killed enteric vaccine in the last 8 weeks.