An Open Label Non-inferiority Trial Assessing Vibriocidal Response of a Killed Bivalent Oral Cholera Vaccine Regimen following a Five Year Interval in Kolkata, India

Oral killed cholera vaccines for preventing cholera

BACKGROUND

Cholera causes acute watery diarrhoea and death if not properly treated. Outbreaks occur in areas with poor sanitation, including refugee camps. Several vaccines have been developed and tested over the last 50 years. This is an update of a Cochrane review, originally published in 1998, which explored the effects of all vaccines for preventing cholera. This review examines oral vaccines made from killed bacteria.

OBJECTIVES

To assess the effectiveness and safety of the available World Health Organization (WHO)-prequalified oral killed cholera vaccines among children and adults.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register; CENTRAL, MEDLINE; Embase; LILACS; and two trials registers (February 2023).

SELECTION CRITERIA

We included randomized controlled trials (RCTs), including cluster-RCTs. There were no restrictions on the age and sex of the participants or the setting of the study. We considered any available WHO-prequalified oral killed cholera vaccine as an intervention. The control group was given a placebo, another vaccine, or no vaccine. The outcomes were related to vaccine effectiveness and safety. We included articles published in English only.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria and extracted data from included studies. We assessed the risk of bias using the Cochrane ROB 1 assessment tool. We used the generic inverse variance and a random-effects model meta-analysis to estimate the pooled effect of the interventions. We assessed the certainty of the evidence using the GRADE approach. For vaccine effectiveness (VE), we converted the overall risk ratio (RR) to vaccine effectiveness using the formula: VE = (1 - RR) x 100%.

MAIN RESULTS

Five RCTs, reported in 12 records, with 462,754 participants, met the inclusion criteria. We identified trials on whole-cell plus recombinant vaccine (WC-rBS vaccine (Dukoral)) from Peru and trials on bivalent whole-cell vaccine (BivWC (Shanchol)) vaccine from India and Bangladesh. We did not identify any trials on other BivWC vaccines (Euvichol/Euvichol-Plus), or Hillchol. Two doses of Dukoral with or without a booster dose reduces cases of cholera at two-year follow-up in a general population of children and adults, and at five-month follow-up in an adult male population (overall VE 76%; RR 0.24, 95% confidence interval (CI) 0.08 to 0.65; 2 trials, 16,423 participants; high-certainty evidence). Two doses of Shanchol reduces cases of cholera at one-year follow-up (overall VE 37%; RR 0.63, 95% CI 0.47 to 0.85; 2 trials, 241,631 participants; high-certainty evidence), at two-year follow-up (overall VE 64%; RR 0.36, 95% CI 0.16 to 0.81; 2 trials, 168,540 participants; moderate-certainty evidence), and at five-year follow-up (overall VE 80%; RR 0.20, 95% CI 0.15 to 0.26; 1 trial, 54,519 participants; high-certainty evidence). A single dose of Shanchol reduces cases of cholera at six-month follow-up (overall VE 40%; RR 0.60, 95% CI 0.47 to 0.77; 1 trial, 204,700 participants; high-certainty evidence), and at two-year follow-up (overall VE 39%; RR 0.61, 95% CI 0.53 to 0.70; 1 trial, 204,700 participants; high-certainty evidence). A single dose of Shanchol also reduces cases of severe dehydrating cholera at six-month follow-up (overall VE 63%; RR 0.37, 95% CI 0.28 to 0.50; 1 trial, 204,700 participants; high-certainty evidence), and at two-year follow-up (overall VE 50%; RR 0.50, 95% CI 0.42 to 0.60; 1 trial, 204,700 participants; high-certainty evidence). We found no differences in the reporting of adverse events due to vaccination between the vaccine and control/placebo groups.

AUTHORS' CONCLUSIONS

Two doses of Dukoral reduces cases of cholera at two-year follow-up. Two doses of Shanchol reduces cases of cholera at five-year follow-up, and a single dose of Shanchol reduces cases of cholera at two-year follow-up. Overall, the vaccines were safe and well-tolerated. We found no trials on other BivWC vaccines (Euvichol/Euvichol-Plus). However, BivWC products (Shanchol, Euvichol/Euvichol-Plus) are considered to produce comparable vibriocidal responses. Therefore, it is reasonable to apply the results from Shanchol trials to the other BivWC products (Euvichol/Euvichol-Plus).

Immunogenicity and waning immunity from the oral cholera vaccine (Shanchol™) in adults residing in Lukanga Swamps of Zambia

Introduction

In cholera endemic areas, the periodicity of cholera outbreaks remains unpredictable, making it difficult to organize preventive efforts. Lack of data on duration of protection conferred by oral cholera vaccines further makes it difficult to determine when to deploy preemptive vaccination. We report on the immunogenicity and waning of immunity to Shanchol^™ in Lukanga Swamps.

Methods

We enrolled a cohort of 223 participants aged between 18 and 65 years old from whom serum samples were collected at baseline, day 28 before administration of the second dose, and consecutively at 6, 12, 24, 30, 36, and 48 months. Vibriocidal antibody titres were measured and expressed as geometric mean titres. Box plots and 95% CI were computed at each visit for both Inaba and Ogawa. Seroconversion was defined as a four fold or greater increase in antibody titres compared to baseline titres.

Results

Overall, seroconversion against V. cholerae Inaba and Ogawa after 1st dose was 35/134 (26%) and 34/134 (25%) respectively. We observed a statistical difference in seroconversion between the two subgroups of baseline titres (low <80 and high ≥80) for both Inaba (p = 0.02) and Ogawa (p<0.0001). From a baseline of 13.58, anti-Ogawa GMT increased to 21.95 after the first dose, but rapidly waned to 14.52, 13.13, and 12.78 at months 6, 12 and 24 respectively, and then increased to 13.21, 18.67 and 23.65 at months 30, 36 and 48 respectively. A similar trend was observed for anti-Inaba GMT across the same time points.

Conclusion

We found that Shanchol^™ was immunogenic in our study population and that vibriocidal antibodies may not be a good marker for long-term immunity. The observed rise in titres after 36 months suggests natural exposure, and this may be a critical time window opening for natural transmission in an endemic areas. We recommend re-vaccination at this time point in high risk areas.

A dysbiotic gut microbiome suppresses antibody mediated-protection against Vibrio cholerae

Cholera is a severe diarrheal disease that places a significant burden on global health. Cholera's high morbidity demands effective prophylactic strategies, but oral cholera vaccines exhibit variable efficacy in human populations. One contributor of variance in human populations is the gut microbiome, which in cholera-endemic areas is modulated by malnutrition, cholera, and non-cholera diarrhea. We conducted fecal transplants from healthy human donors and model communities of either human gut microbes that resemble healthy individuals or those of individuals recovering from diarrhea in various mouse models. We show microbiome-specific effects on host antibody responses against Vibrio cholerae, and that dysbiotic human gut microbiomes representative of cholera-endemic areas suppress the immune response against V. cholerae via CD4+ lymphocytes. Our findings suggest that gut microbiome composition at time of infection or vaccination may be pivotal for providing robust mucosal immunity, and suggest a target for improved prophylactic and therapeutic strategies for cholera.

Augmented immune responses to a booster dose of oral cholera vaccine in Bangladeshi children less than 5 years of age: Revaccination after an interval of over three years of primary vaccination with a single dose of vaccine

We have earlier reported that a single dose of oral cholera vaccine (OCV) is protective in adults and children ≥5 years of age and sustained for 2 years. We enrolled participants (n = 240) from this study, between March-September 2017, over 3 years after receiving a primary single dose. Immune responses were measured in placebo group (Primary Immunization group: PI) and compared with those who received a single dose (Booster Immunization group: BI). The children were 4 to <5 years, 5 to <18 years and adults >18 years. Blood was collected at day 0 (before vaccination) and after receiving 1st and 2nd doses of OCV. Overall, the BI and PI groups showed vibriocidal antibody response after 1st and 2nd dose of vaccination in all age groups to V. cholerae O1 and O139. Young children in the BI group showed significantly higher vibriocidal antibody response two weeks after receiving the first dose as compared to PI group to LPS. Elevated plasma IgA responses to LPS after the first dose were observed among the BI group compared to the PI group among the young children. Mucosal antibody responses measured in fecal extracts showed similar increases as that of vibriocidal and LPS responses in the BI group. These results suggest a single boosting dose of OCV generated immune response in primed population >5 years of age who had earlier received OCV. However, young children who had received OCV earlier, boosting after a single dose, resulted in increased immune responses compared to the PI group. Further studies are needed to assess protection obtained from different strategies, especially for young children and to determine the numbers of primary and booster doses needed. In addition, more information is needed regarding the optimum interval between primary and booster doses to plan future interventions for cholera control. ClinicalTrials.gov Identifier: NCT02027207.

Trials of the killed oral cholera vaccine (Shanchol) in India and Bangladesh: Lessons learned and way forward

Cholera has been endemic in India and Bangladesh for the greater part of recorded history, giving this region the reputation of being the 'homeland of cholera'. The causative organism Vibrio cholerae O1 has been responsible for large epidemics and pandemics. Bangladesh and India have conducted several sequential studies of Oral Cholera Vaccine (OCV) to ascertain its safety, efficacy, effectiveness, field feasibility and acceptance in high-risk urban populations. The objective of this article is to illustrate the experience of OCV use in these endemic settings, its major challenges, and how policymakers can grant vaccine licenses as well as implement its use in the national immunization programme. The relevant aspects of the OCV studies, such as boosting the effect of vaccine, single-dose versus double-dose trials and thermal stability of the vaccine during delivery have generated strong evidence for recommendation of vaccine use in these settings. Studies have shown that a single dose is effective for children of five years of age and older age groups. The locally manufactured vaccine in India is thermostable and can be delivered in field settings without use of cold chain. The vaccine delivery is feasible and the protective efficacy (PE) of this vaccine above five years of age against cholera was 53-65%. Administration of an OCV boosting regimen elicits an immune response similar to those who received a two-dose vaccine five years back. OCV can be used as a preemptive measure in endemic settings, in natural calamities and during political instability when there is total disruption as well as collapse of safe water supply, sanitation and hygiene (WASH) facilities and other control measures. Clear identification of areas and target population (who will gain benefit from the OCVs) is required to be developed in endemic settings.

Bivalent oral cholera vaccination induces a memory B cell response to the V. cholerae O1-polysaccharide antigen in Haitian adults

The bivalent killed whole-cell oral cholera vaccine (BivWC) is being increasingly used to prevent cholera. The presence of O-antigen-specific memory B cells (MBC) has been associated with protective immunity against cholera, yet MBC responses have not been evaluated after BivWC vaccination. To address this knowledge gap, we measured V. cholerae O1-antigen MBC responses following BivWC vaccination. Adults in St. Marc, Haiti, received 2 doses of the BivWC vaccine, Shanchol, two weeks apart. Participants were invited to return at days 7, 21, 44, 90, 180 and 360 after the initial vaccination. Serum antibody and MBC responses were assessed at each time-point before and following vaccination. We observed that vaccination with BivWC resulted in significant O-antigen specific MBC responses to both Ogawa and Inaba serotypes that were detected by day 21 and remained significantly elevated over baseline for up to 12 months following vaccination. The BivWC oral cholera vaccine induces durable MBC responses to the V. cholerae O1-antigen. This suggests that long-term protection observed following vaccination with BivWC could be mediated or maintained by MBC responses.

Oral cholera vaccines are being increasingly used throughout the world as a key component of cholera prevention programs. While several recent studies suggest oral cholera vaccines may provide durable protection, the potential mechanism that generates this long lasting immune memory and protection are unknown. Unlike antibody and antibody secreting cell responses, memory B cells are thought to be an important part of the immune responses because although these cells do not produce antibody, they are long lived and can be rapidly stimulated to produce antibodies upon re-exposure to infection. Previous studies have shown that memory B cell responses to the Vibrio cholerae O-antigen are associated with protection against cholera infection. In this study, we found that oral cholera vaccine generated long lasting antibody and memory B cell responses to the Vibrio cholerae O-antigen that remained elevated for 6 to 12 months. These findings show that oral cholera vaccination does induce a strong memory B cell response, which could play a role in the generation and maintenance of long-term protection following BivWC vaccination.

Challenges for programmatic implementation of killed whole cell oral cholera vaccines for prevention and control of cholera: a meta-opinion

INTRODUCTION

Cholera remains a public health threat. The development of safe, effective, easy-to-administer, heat-stable, and cheap killed whole cell oral cholera vaccines (OCVs) has provided an additional tool to counter cholera. In this meta-opinion, we review the challenges of delivering OCVs through the existing public health infrastructure in vulnerable areas.

AREAS COVERED

We provide an overview of the available vaccines against cholera, the existing evidence about the effectiveness of a two-dose as well as a single-dose OCV strategy. We also highlight the experience from the public health campaigns for OCV deployment.

EXPERT OPINION

Several public health experiences have shown the feasibility of incorporating OCVs into the public health response against cholera. Combined with a comprehensive water, sanitation, and hygiene (WaSH) improvement plan, OCVs need to be deployed in identified vulnerable areas, targeting the highest risk groups first. Vaccination programs should not be deployed in lieu of investments in WaSH services, but as a complimentary service in a comprehensive, cholera control intervention package. It has been a challenge to have high two-dose coverage across all eligible recipients, necessitating the adoption of innovative strategies to boost coverage. Longer intervals between doses may help to overcome resource and logistical limitations enabling higher coverage.

Bivalent oral cholera vaccine in participants aged 1 year and older in the Dominican Republic: A phase III, single-arm, safety and immunogenicity trial

The Dominican Republic, historically non-endemic for cholera, is experiencing an ongoing cholera epidemic. We assessed the safety and immunogenicity of two doses of the killed bivalent (O1 and O139) whole-cell oral cholera vaccine (OCV) on day (D)0 and D14 in healthy participants aged ≥1 year. Immediate unsolicited systemic adverse events (AEs) were monitored up to 30 minutes and solicited systemic reactions, up to 7 days after each vaccination. Unsolicited AEs were recorded up to D14 (post-dose 1) and 30 days post-dose 2. A vibriocidal antibody assay with microtiter technique was used to measure serum antibodies to V. cholerae strains (O1 El Tor Inaba, O1 El Tor Ogawa, O139) on D0, D14 and D28. Geometric mean titers (GMTs) and seroconversion (≥4-fold increase from D0) rates were calculated. We recruited 336 participants; 112 in three age groups (1–4, 5–14 and ≥15 years). No safety concerns were observed. GMTs increased from baseline for all serotypes, with marked increases for O1 Inaba and Ogawa post-dose 1. Post-dose 2 GMTs tended to be equal or slightly lower, with ranges: O1 Inaba, 283 (95% confidence interval 191–419) to 612 (426–880); O1 Ogawa, 346 (223–536) to 754 (553–1028); and O139, 20.3 (13.5–30.6) to 43.8 (30.1–63.7). Seroconversion rates post-dose 2 for O1 Inaba and Ogawa were high (≥87%) for all age groups. OCV demonstrated an acceptable safety profile and robust immunogenicity in these participants, in-line with previous observations in epidemic and endemic settings.This study is registered on www.clinicaltrials.gov (NCT02434822).

Immunogenicity and Protection From a Single Dose of Internationally Available Killed Oral Cholera Vaccine: A Systematic Review and Metaanalysis

In addition to improved water supply and sanitation, the 2-dose killed oral cholera vaccine (OCV) is an important tool for the prevention and control of cholera. We aimed to document the immunogenicity and protection (efficacy and effectiveness) conferred by a single OCV dose against cholera. The metaanalysis showed that an estimated 73% and 77% of individuals seroconverted to the Ogawa and Inaba serotypes, respectively, after an OCV first dose. The estimates of single-dose vaccine protection from available studies are 87% at 2 months decreasing to 33% at 2 years. Current immunologic and clinical data suggest that protection conferred by a single dose of killed OCV may be sufficient to reduce short-term risk in outbreaks or other high-risk settings, which may be especially useful when vaccine supply is limited. However, until more data suggest otherwise, a second dose should be given as soon as circumstances allow to ensure robust protection.

Efficacy of a bivalent killed whole-cell cholera vaccine over five years: a re-analysis of a cluster-randomized trial

Background

Oral cholera vaccine (OCV) is a feasible tool to prevent or mitigate cholera outbreaks. A better understanding of the vaccine’s efficacy among different age groups and how rapidly its protection wanes could help guide vaccination policy.

Methods

To estimate the level and duration of OCV efficacy, we re-analyzed data from a previously published cluster-randomized, double-blind, placebo controlled trial with five years of follow-up. We used a Cox proportional hazards model and modeled the potentially time-dependent effect of age categories on both vaccine efficacy and risk of infection in the placebo group. In addition, we investigated the impact of an outbreak period on model estimation.

Results

Vaccine efficacy was 38% (95% CI: -2%,62%) for those vaccinated from ages 1 to under 5 years old, 85% (95% CI: 67%,93%) for those 5 to under 15 years, and 69% (95% CI: 49%,81%) for those vaccinated at ages 15 years and older. Among adult vaccinees, efficacy did not appear to wane during the trial, but there was insufficient data to assess the waning of efficacy among child vaccinees.

Conclusions

Through this re-analysis we were able to detect a statistically significant difference in OCV efficacy when the vaccine was administered to children under 5 years old vs. children 5 years and older. The estimated efficacies are more similar to the previously published analysis based on the first two years of follow-up than the analysis based on all five years.

Trial registration

ClinicalTrials.gov identifier NCT00289224

Electronic supplementary material

The online version of this article (10.1186/s12879-018-2981-4) contains supplementary material, which is available to authorized users.

A rapid qualitative assessment of oral cholera vaccine anticipated acceptability in a context of resistance towards cholera intervention in Nampula, Mozambique

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Political resistance impacts potential OCV acceptability.

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Perceived vulnerability to cholera overrides rationale for OCV hesitancy.

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Case-by-case preemptive studies maximize public health intervention acceptability.

Introduction

While planning an immunization campaign in settings where public health interventions are subject to politically motivated resistance, designing context-based social mobilization strategies is critical to ensure community acceptability. In preparation for an Oral Cholera Vaccine campaign implemented in Nampula, Mozambique, in November 2016, we assessed potential barriers and levers for vaccine acceptability.

Methods

Questionnaires, in-depth interviews, and focus group discussions, as well as observations, were conducted before the campaign. The participants included central and district level government informants (national immunization program, logistics officers, public health directors, and others), community leaders and representatives, and community members.

Results

During previous well chlorination interventions, some government representatives and health agents were attacked, because they were believed to be responsible for spreading cholera instead of purifying the wells. Politically motivated resistance to cholera interventions resurfaced when an OCV campaign was considered. Respondents also reported vaccine hesitancy related to experiences of problems during school-based vaccine introduction, rumors related to vaccine safety, and negative experiences following routine childhood immunization. Despite major suspicions associated with the OCV campaign, respondents’ perceived vulnerability to cholera and its perceived severity seem to override potential anticipated OCV vaccine hesitancy.

Discussion

Potential hesitancy towards the OCV campaign is grounded in global insecurity, social disequilibrium, and perceived institutional negligence, which reinforces a representation of estrangement from the central government, triggering suspicions on its intentions in implementing the OCV campaign. Recommendations include a strong involvement of community leaders, which is important for successful social mobilization; representatives of different political parties should be equally involved in social mobilization efforts, before and during campaigns; and public health officials should promote other planned interventions to mitigate the lack of trust associated with perceived institutional negligence. Successful past initiatives include public intake of purified water or newly introduced medication by social mobilizers, teachers or credible leaders.

The African cholera surveillance network (Africhol) consortium meeting, 10-11 June 2015, Lomé, Togo

The fifth annual meeting of the African cholera surveillance network (Africhol) took place on 10–11 June 2015 in Lomé, Togo. Together with international partners, representatives from the 11 member countries -Cameroon, Côte d’Ivoire, Democratic Republic of Congo, Guinea, Kenya, Mozambique, Nigeria, Tanzania, Togo, Uganda, Zimbabwe- and an invited country (Malawi) shared their experience. The meeting featured three sessions: i) cholera surveillance, prevention and control in participating countries, ii) cholera surveillance methodology, such as cholera mapping, cost-effectiveness studies and the issue of overlapping epidemics from different diseases, iii) cholera laboratory diagnostics tools and capacity building. The meeting has greatly benefitted from the input of technical expertise from participating institutions and the observations emerging from the meeting should enable national teams to make recommendations to their respective governments on the most appropriate and effective measures to be taken for the prevention and control of cholera.

Recommendations for future activities included collecting precise burden estimates in surveillance sites; modeling cholera burden for Africa; setting up cross-border collaborations; strengthening laboratory capacity for the confirmation of suspected cholera cases and for vaccine impact assessment in settings where oral cholera vaccine would be used; adapting cholera surveillance to concurrent issues (e.g., Ebola); and developing national cholera control plans including rationale vaccination strategies together with other preventive and control measures such as improvements in water, sanitation and hygiene (WASH).