Manufacturers of oral cholera vaccine (OCV) recommend a 7- or 14-days interval between two doses. To carry out two rounds of mass vaccination within this delay is not always feasible and many campaigns implemented to date have used a longer interval. Recent evidence indicates that an extended interval between OCV doses might result in equivalent seroconversion rates and in an improved boosting of mucosal immune responses following the second dose. To guide future OCV vaccination campaigns and improve cholera prevention, it is important to demonstrate the non-inferior immune response of an extended interval between OCV doses.~The Investigators aim to demonstrate the non-inferiority of the humoral immune response between individuals receiving a second Euvichol-Plus® pre-qualified OCV dose either 6 or 12 months after the initial dose and individuals receiving a second pre-qualified OCV dose 14 days after the initial dose. The humoral immune response will be assessed as the post-vaccination titer of serum vibriocidal antibodies at 14 days post-2nd dose vaccination. Secondary outcomes include the comparison of the overall rate of vibriocidal seroconversion 14 days after either the first or the second vaccine dose. A subsample of individuals ≥ 18 years will have additional serological evaluation to characterize the kinetics of their antibody responses up to 6 months after the second OCV vaccine dose. Although the vaccine has an established and safe profile, occurrence of adverse events and serious adverse events following vaccination will be assessed (safety evaluation).~The study will be an open-label, randomized, controlled, non-inferiority immunogenicity trial comparing the humoral immune responses to OCV in two interventions arms (6 and 12 months interval between OCV doses) compared with a control arm (standard 14-day interval). In each arm, the aim is to recruit 152 individuals aged 1 to 40 year-old eligible for OCV vaccination from the general population (ie. 456 individuals in total). The sub-sample allowing characterizing the kinetics of the humoral response up to 6 months after the administration of the second dose will include 38 participants in each intervention and control arm, among the participants aged ≥ 18 years. In total, 456 individuals will be recruited.~The study will be conducted in Conakry, in the Republic of Guinea. Participants will be primarily enrolled in the commune of Dixinn on a voluntary basis. All participants in the intervention and control arms will be invited to a first visit for assessment of eligibility and 1st OCV dose, followed by a visit 14 days after the 1st OCV dose for blood sampling. According to the study arm, the 2nd OCV dose will be administered at 14 days, 6 months or 1 year after the 1st dose and will be followed by a visit 14 days later for blood sampling. Participants in the sub-study will be invited to additional study visits (up to twelve visits in total) for blood sampling. At each visit, blood will be drawn for immunologic analyses.
Immune response to a delayed second dose of oral cholera vaccine~A randomized, controlled, non-inferiority immunogenicity trial in Conakry, The Republic of Guinea