Extended dosing schedules for the oral cholera vaccine in Kenya

Inclusion Criteria:

* Residents of Mukuru, Nairobi, Kenya
* Individuals aged 1 year and above
* Voluntary written informed consent for study participation provided by an individual or his/her legally acceptable representative. Children aged 13 years and above will also provide assent, with parental permission required for all children.
* Ability to comply with study requirements and attend follow-up visits during the study period.

Participants must be in good health, as determined by medical history, physical examination, and the clinical judgment of the investigators. Clinical judgment will consider factors such as the absence of acute illness or, uncontrolled or severe chronic conditions that may affect participation in the study.

* Lactating women may be enrolled following clinical assessment and informed consent. The vaccine contains killed, formalin-inactivated bacteria that are not systemically absorbed and act locally in the gastrointestinal tract.

Exclusion Criteria:

* Known history of hypersensitivity reactions to other vaccines.
* Pregnant women, due to differences in immune response. A pregnancy test will be administered to all female participants who have reached menarche and are under 50 years.
* Reported diarrhea or abdominal pain lasting 2 weeks or longer within 6 months prior to study initiation; to avoid confounding the vaccine's effects with pre-existing conditions.
* Received a cholera vaccine in the last 24 months: Ensures that the study assesses the vaccine in question without interference from prior vaccinations.
* History of cholera disease in the last 24 months: Recent history of cholera infection can interfere with the measurement of vaccine response.
* Severely malnourished individuals as determined by mid-upper arm circumference (MUAC) and age-specific body mass index (BMI) measurements: malnutrition can affect immune response and vaccine efficacy. In children below 510 years, severe malnutrition will be defined as MUAC \< 11.5 cm, for older children (age 5 - 17y) severe malnutrition will be defined as BMI-for-age z score \< -3 (WHO Child Growth Standards), for children \<10y, presence of bilateral pitting oedema will be considered indicative of severe malnutrition. For adults (18y and above), severe malnutrition will be while in older children and adults it will be defined as BMI \< 16.
* Non-HIV/AIDS immunosuppressive condition or on immunosuppressive therapy: Such conditions can significantly alter vaccine response.
* Presence of bleeding disorders or medical contraindication for blood draws: To ensure participant safety during blood collection.
* Participation in another clinical trial with investigational product dosing within 6 months prior to study initiation.
* An individual thought to have difficulty in participating in the study due to severe chronic diseases, based on the judgment of the investigator.
* An individual thought to have difficulty participating in the study due to reasons, such as significant logistical constraints, or communication barriers, or likely to be away for a period of at least 3 consecutive months in the first 6 months of enrollment based on the judgment of the investigator.