Cholera is a re-emerging infectious disease that causes significant morbidity and mortality in populations lacking access to safe drinking water and sanitation. Provision of safe drinking water and food, establishment of adequate sanitation, and implementation of personal and community hygiene constitute the main public health interventions against cholera. These measures cannot be implemented fully in the near future in most cholera-endemic areas. Improvements to water and sanitation require substantial long-term investments, commitment from the local government and often take years to implement. In the meantime, a safe, effective, and affordable vaccine would be a useful tool for cholera prevention and control.~Considerable progress has been made during the last decade in the development of new generation oral cholera vaccines against cholera. A monovalent (anti-O1) WC-rBS oral killed cholera vaccine with a B-subunit was developed by Professor Jan Holmgren in Sweden and is sold primarily as a traveler's vaccine; and is only WHO pre-qualified vaccine till date. A version of this vaccine that lacks the B subunit and is considerably less expensive to produce (whole-cell only) and which is now bivalent (O1 and O139), has been produced and used exclusively in Vietnam, making it the first oral cholera vaccine used primarily for endemic populations.~To internationalize the use of this improved vaccine, its production technology was modified to comply with the WHO Manufacturing practices (cGMP) standards before its manufacturing technology was transferred to an Indian manufacturing company Shantha Biotechnics Limited by the International Vaccine Institute. The modified killed bivalent oral cholera vaccine has been recently licensed by the Drugs Controller General of India (DCGI) to the Shantha Biotechnics Limited and being marketed as Shancol ® after phase II and Phase III clinical trials. It is administered orally in 2 liquid doses (without need of any buffer solution) 14 days for individuals aged 1 year and above. It was found safe, effective and provided 67% protection after two years in a placebo-controlled, randomized trial in Kolkata, India.~Despite the recent licensure, there are remaining questions that need to be answered that would be vital in deploying the vaccine including optimization of dosing regimen. A previous study performed in Kolkata revealed that two doses of the vaccine when given 14 days apart did not result in higher immune response after the first dose, contrary to earlier findings with the Swedish vaccine. This new finding may be due to the higher lipopolysaccharide (LPS) content of the modified vaccine which may have elicited sufficient immune response that it effectively blocks subsequent antigen presentation with the second dose of the vaccine.~In order to assess if immune responses will be boosted if we prolong the interval between dosing of the modified killed oral cholera vaccine, a Phase II double-blind, controlled, randomized trial to evaluate two different dosing interval schedules for the two-dose regimen will be conducted. This study will compare the immune responses following 14-day and 28-day dosing intervals. In addition to the 356 subjects for the main study, 30 subjects will be enrolled to explore the possibility of any other immunological marker for vibrio cholera infection.
The absence of a boosting response after a 14 day interval with the two-dose regimen of the modified killed oral cholera vaccine raises the possibility that a longer dosing interval may be required to observe a boost in the immune response. This study will compare the immune responses following 14-day and 28-day dosing intervals.