The reactive cholera vaccination campaign in urban Dhaka in 2022: experience, lessons learned and future directions

Introduction

An upsurge of diarrheal cases occurred in Dhaka, Bangladesh, with approximately 30% of the cases being identified as cholera in 2022. To combat this situation, a reactive Oral Cholera Vaccination campaign was organized in five highly cholera-affected areas of Dhaka city. The paper is a descriptive tale of experience gathering, organization and implementation of reactive oral cholera vaccination campaign.

Study design

This is a descriptive report of a reactive oral cholera vaccination campaign.

Methods

Population density maps were generated using GIS technology before launching the campaign. The target population comprised individuals aged over one year, excluding pregnant women, totaling 2,374,976 people residing in above mentioned areas. The campaign utilized Euvichol-Plus, an OCV with adherence to the necessary cold chain requirements. Total 700 teams, each consisting of six members, were deployed across the five zones. The campaign was conducted in two rounds, where first round took place in June-July 2022, followed by second round in August 2022. During the campaign, data on adverse events following immunization (AEFI) was collected. Expert teams from various government and non-government organizations monitored regularly and ensured the campaign's success.

Results

The first round achieved a coverage rate of 99%, whereas in the second round, 86.3% of individuals among the first dose recipients. During the campaigns, a total of 57 AEFIs were reported.

Conclusions

This campaign serves as a model for a multispectral approach in combating cholera epidemics, highlighting the collaborative efforts of policymakers, health authorities, local communities, and health partners.

The interplay between WASH practices and vaccination with oral cholera vaccines in protecting against cholera in urban Bangladesh: Reanalysis of a cluster-randomized trial

The current global initiative to end Cholera by 2030 emphasizes the use of oral cholera vaccine (OCV) combined with feasible household Water-Sanitation-Hygiene (WASH) interventions. However, little is known about how improved WASH practices and behaviors and OCV interact to reduce the risk of cholera. We reanalyzed two arms of a cluster-randomized trial in urban Bangladesh, to evaluate the effectiveness of OCV given as a 2-dose regimen. One arm (30 clusters, n = 94,675) was randomized to vaccination of persons aged one year and older with OCV, and the other arm (30 clusters, n = 80,056) to no intervention. We evaluated the prevention of cholera by household WASH, classified at baseline using a previously validated rule, and OCV over 2 years of follow-up. When analyzed by assignment to OCV clusters rather than receipt of OCV, in comparison to persons living in "Not Better WASH" households in the control clusters, reduction of severe cholera (the primary outcome) was similar for persons in "Not Better WASH" households in vaccine clusters (46%, 95% CI:24,62), for persons in "Better WASH" households in the control clusters (48%, 95% CI:25,64), and for persons in "Better WASH" households in the vaccine clusters (48%, 95% CI:16,67). In contrast, when analyzed by actual receipt of a complete OCV regimen, , in comparison to persons in "Not Better WASH" households in the control clusters, protection against severe cholera increased steadily from 39% (95% CI:13,58) in residents of "Better WASH" households in the control clusters to 57% (95% CI:35,72) in vaccinated persons in "Not Better WASH" households to 63% (95% CI:21,83) in vaccinated persons in "Better WASH" households. This analysis suggests that improved household WASH and OCV received may interact to provide greater protection against cholera. However, the divergence between findings related to intent to vaccinate versus those pertaining to actual receipt of OCV underscores the need for further research on this topic.

Travel vaccines are strongly associated to reduced mortality in prostate cancer patients - a real effect or residual confounding?

Repurposing of existing drugs and vaccines for diseases that they were not originally intended for is a promising research field. Recently there has been evidence that oral cholera vaccine might be used in the treatment of inflammatory disease and some common cancers. Specifically, Ji et al showed that the administration of cholera vaccine after a prostate cancer diagnosis reduced prostate cancer specific mortality rates by almost 50%. In a cohort of men from Stockholm, Sweden, with more detailed cancer data and a higher coverage of exposure to vaccine, we replicated these findings using a marginal structural Cox model. We showed that administration of cholera vaccine after prostate cancer diagnosis is associated with a significant reduction in mortality (HR 0.46, 95% CI 0.31-0.69, p-value 0.0001) even after adjusting for all known confounders. However, the same effect (or even stronger) could be seen for several other traveling vaccines and malaria prophylaxis. Therefore, we conclude that this effect is most likely due to a healthy traveler bias and is an example of residual confounding.

Oral MucoRice-CTB vaccine is safe and immunogenic in healthy US adults

MucoRice-CTB is a promising cold-chain-free oral cholera vaccine candidate. Here, we report a double-blind, randomized, placebo-controlled, phase I study conducted in the USA in which vaccination with the 6-g dose of MucoRice-CTB induced cross-reactive antigen-specific antibodies against the B subunit of cholera toxin (CTB) and enterotoxigenic Escherichia coli heat-labile enterotoxin without inducing serious adverse events. This dosage was acceptably safe and tolerable in healthy men and women. In addition, it induced a CTB-specific IgA response in the saliva of two of the nine treated subjects; in one subject, the immunological kinetics of the salivary IgA were similar to those of the serum CTB-specific IgA. Antibodies from three of the five responders to the vaccine prevented CTB from binding its GM1 ganglioside receptor. These results are consistent with those of the phase I study in Japan, suggesting that oral MucoRice-CTB induces neutralizing antibodies against diarrheal toxins regardless of ethnicity.

A reactive vaccination campaign with single dose oral cholera vaccine (OCV) during a cholera outbreak in Cameroon

BACKGROUND

Cameroon chose Oral Cholera Vaccine (OCV) mass vaccination campaign in addition to other interventions to respond to outbreaks since 2015. There is still a persistent controversy on the effectiveness of reactive OCV mass vaccination campaign.

OBJECTIVE

This article aimed to share evidence-based observations on the effect of a reactive single-dose OCV mass vaccination campaign on cholera cases in Cameroon.

METHODS

Health area centered risk analysis was used to identify nine high risk health areas among four health districts in the |North Region as hotspots. About 537,274 people at risk of cholera transmission one year of age and above including pregnant women were eligible to receive OCV. A total of 537,279 doses of OCV was deployed for vaccination from August 1-5, 2019 through door-to-door strategy for urban health districts, and fixed/ temporary fixed posts strategies for rural health districts.

RESULTS

The overall vaccination coverage was 99.9%. Vaccine wastage rate was less than 0.5% (0.0011%). Independent monitoring showed vaccination coverage at 97.2%. The 2019 epidemic curve went down after OCV intervention on the contrary to that in the year 2018 at the same period. After OCV intervention, cholera cases dropped from about 10.5 to 9.3 cases per week at the regional level while at the district level, they dropped from 5.3 to 2.1, 2.2 to 1.7, 0.6 to 0 and 1.7 to 1.5 cases per week respectively for Garoua, Garoua II, Tchollire and Pitoa. Though not statistically significant (p = 1.4, α = 0.05), cases per 1000 population seemed to remain unchanged among OCV zones (0.32/1000) and non-OCV zones (0.31/1000) in 2018 while they increased from 0.37 (OCV zones) to 0.53 (non-0CV zones) cases per 1000 population in 2019.

CONCLUSION

There might have been a general trend in the reduction of the number of new cases after a reactive single-dose OCV campaign.

Comparative whole-genome and proteomics analyses of the next seed bank and the original master seed bank of MucoRice-CTB 51A line, a rice-based oral cholera vaccine

BACKGROUND

We have previously developed a rice-based oral vaccine against cholera diarrhea, MucoRice-CTB. Using Agrobacterium-mediated co-transformation, we produced the selection marker-free MucoRice-CTB line 51A, which has three copies of the cholera toxin B subunit (CTB) gene and two copies of an RNAi cassette inserted into the rice genome. We determined the sequence and location of the transgenes on rice chromosomes 3 and 12. The expression of alpha-amylase/trypsin inhibitor, a major allergen protein in rice, is lower in this line than in wild-type rice. Line 51A was self-pollinated for five generations to fix the transgenes, and the seeds of the sixth generation produced by T5 plants were defined as the master seed bank (MSB). T6 plants were grown from part of the MSB seeds and were self-pollinated to produce T7 seeds (next seed bank; NSB). NSB was examined and its whole genome and proteome were compared with those of MSB.

RESULTS

We re-sequenced the transgenes of NSB and MSB and confirmed the positions of the three CTB genes inserted into chromosomes 3 and 12. The DNA sequences of the transgenes were identical between NSB and MSB. Using whole-genome sequencing, we compared the genome sequences of three NSB with three MSB samples, and evaluated the effects of SNPs and genomic structural variants by clustering. No functionally important mutations (SNPs, translocations, deletions, or inversions of genic regions on chromosomes) between NSB and MSB samples were detected. Analysis of salt-soluble proteins from NSB and MSB samples by shot-gun MS/MS detected no considerable differences in protein abundance. No difference in the expression pattern of storage proteins and CTB in mature seeds of NSB and MSB was detected by immuno-fluorescence microscopy.

CONCLUSIONS

All analyses revealed no considerable differences between NSB and MSB samples. Therefore, NSB can be used to replace MSB in the near future.

Pregnancy outcomes after a mass vaccination campaign with an oral cholera vaccine: a systematic review and meta-analysis

BACKGROUND

Cholera has harmful effects on the fetus but safety data on the oral cholera vaccine in pregnant women are controversial.

OBJECTIVES

We conducted the first meta-analysis of studies in pregnant women comparing the effect of oral cholera vaccination on pregnancy outcomes with unvaccinated women. Outcomes of interest were adverse pregnancy outcome, miscarriage, stillbirth, preterm delivery, low birthweight, abortion and malformation.

SEARCH STRATEGY

The search was run in MEDLINE/PubMed, SCOPUS and Embase databases from inception up to December 2019.

SELECTION CRITERIA

Inclusion criteria were: (1) studies that investigated the association between oral cholera vaccines and adverse pregnancy outcomes; (2) studies that reported outcomes with appropriate estimates; and (3) studies that contained an unvaccinated control group.

DATA COLLECTION AND ANALYSIS

A random-effects model (DerSimonian and Laird) was run to evaluate the overall treatment effect (relative risk, RR). The PRISMA statement was followed in reporting this meta-analysis.

MAIN RESULTS

Five studies included in meta-analysis with 5584 women (2920 exposed and 2664 not exposed). No significant increase in adverse pregnancy outcome (RR 1.03, 95% CI 0.79-1.34), miscarriage (RR 1.15, 95% CI 0.84-1.57) or stillbirth (RR 1.11, 95% CI 0.69-1.80) following cholera vaccine administration was found compared with control group. There was also no association with an increased risk of preterm delivery (RR 0.61, 95% CI 0.35-1.06) low birthweight (RR 0.84, 95% CI 0.56- 1.26), accidental abortion (RR 1.02, 95% CI 0.77-1.35) or malformation (RR 0.70, 95% CI 0.22-2.25).

CONCLUSIONS

This study shows no evidence of an association between oral cholera vaccination and adverse pregnancy outcomes. The findings do not rigorously exclude the possibility that the vaccine protocol may result in some degree of harm.

TWEETABLE ABSTRACT

There is no evidence of an association between oral cholera vaccination and adverse pregnancy outcomes. The findings do not rigorously exclude the possibility that the vaccine protocol may result in some degree of harm.

Oral cholera vaccination coverage in an acute emergency setting in Somalia, 2017

The first oral cholera vaccination (OCV) campaign in Somalia was implemented between March and October 2017. It was the first time the Ministry of Health had introduced and used OCV as part of the cholera prevention and control strategies. The Ministry of Health aimed to cover 1.1 million people ≥ 1 year with 2 doses of the OCV in 11 high-risk districts. Overall, 2-dose administrative OCV coverage in all targeted districts was 95.5%. Following the campaign, a random sample survey was conducted in 9 out of 11districts to evaluate coverage, awareness, reasons for non-vaccination, the water and sanitation status of households, and any resulting adverse events. The survey was conducted in 2 phases. Of the 3,715 eligible individuals in the first phase, 92.5% (95% CI 91.4-93.6%) received 2 doses of the OCV and 7.0% (95% CI 6.0-8.2%) 1 dose. In the second phase, of 1,926 individuals, 94.1% (95% CI 92.9-95.1%) received 2 doses and 2.6% (95% CI 2.0-3.4%) 1 dose. Despite challenges, this experience shows that OCV campaigns can be implemented in acute humanitarian settings through existing immunization structures.

Current and future cholera vaccines

Cholera remains a major global public health problem that is primarily linked to insufficient access to safe water and proper sanitation. Oral Cholera Vaccine (OCV) has been recommended as an additional public health tool along with WASH in cholera endemic countries and in areas at risk for outbreaks. The new generation OCV is safe and offers good protection in older children and adults while limited protection in younger children less than five years of age has been observed. The combination of direct vaccine protection and vaccine herd immunity effects makes OCV highly cost-effective and, therefore, attractive for use in developing countries. Additionally, in recent studies OCV was safe in pregnant women, supporting its use in pregnant women in cholera endemic countries. However, knowledge need to be developed for current vaccines for their prolonged duration of protection and vaccines need improvements for better immune response in younger children. A single dose vaccination regimen would be more cost-effective and easier to deliver. Recent approaches have focused on designing genetically attenuated cholera strains for use in single-dose cholera vaccines. The global demand for OCV has been boosted by the WHO recommendation to use OCV and is driven largely by epidemics and outbreaks and has been increasing due to the availability of cheaper easy-to-use vaccines, feasibility of mass OCV vaccination campaigns, demonstration of protection to underserved population in precarious situations, and vaccine costs being borne by Gavi (Vaccine Alliance). For rapid access in emergency and equitable distribution of OCV in cholera-endemic low-income countries, a global OCV stockpile was established in 2013 with support from the Global Alliance for Vaccines and Immunization. The three WHO-prequalified vaccines are Dukoral®, Shanchol™, Euvichol® (and Euvichol® Plus presentation), the latter two being included in the stockpile.

Contrasts, contradictions and control of cholera

Cholera has been extremely pervasive during the past four decades and continues to remain a significant public health concern. The disease has plagued humankind in the form of seven pandemics since the last two centuries. There is considerable scientific evidence based on research on cholera and its etiologic agent Vibrio cholerae, however we are still unable to accurately forecast and pre-empt the occurrence of cholera outbreaks. The commentary discusses the contrasts and contradictions of cholera, its control and its unpredictable nature. Through a multi-sectoral approach and broad stakeholder collaboration cholera control is possible with meticulous country-level planning for early detection and response to outbreaks. The commentary reiterates that every potential death on account of cholera is preventable because of the available knowledge and tools to effectively prevent and treat cholera.

Oral cholera vaccine delivery strategy in India: Routine or campaign?-A scoping review

Oral Cholera Vaccine (OCV) has been recognized as an adjunct tool for prevention and control of cholera. However, policy directions are currently unavailable in India to guide the vaccine delivery. We conducted a scoping review to inform the policy about the scopes and challenges of different strategic choices of OCV delivery in India in light of current evidences, highlighting the scope of new research.

METHODS

Adopting the Arksey and O'Malley Framework for review, we searched for literatures on "efficacy", "effectiveness", and "cost" of oral cholera vaccine delivery through different strategies in Pubmed and Scopus.

RESULTS

We found that the protective efficacy of OCV depends on its coverage. Evidence on effectiveness of OCV are available for both reactive and pre-vaccination campaigns. Reactive high-risk vaccination is more effective than reactive ring and mass vaccination. Pre-vaccination campaigns are more effective than reactive vaccination when vaccine availability is adequate. Pre-vaccination through school campaigns in 1-14 years age group have been cost effective in India. Vaccination campaigns in under-5 children are also cost effective in spite of low efficacy due to the scope of averting a higher number of cases. However, no evidence is available regarding efficacy and effectiveness of OCV in children <1 year as well as the effectiveness of delivering OCV through routine immunization.

CONCLUSION

Little evidence exist to depict mass-campaign as more economic and effective than routine expanded programme on immunization (EPI) session for delivery of OCV. Considering operational feasibility, it needs to be explored whether OCV delivery strategy is compatible with India's current EPI, if it can be introduced in routine immunization at measles containing vaccine age-schedule, optionally preceded by a campaign in targeted hot-spots in the 1-14 year age-group. Safety and efficacy data of OCV during infancy as well as hot-spot surveillance are pre-requisites for formulation of such EPI policy.

Comparison of the immunogenicity of Dukoral® oral cholera vaccine between renal transplant recipients on either a calcineurin inhibitor or mycophenolate - A controlled trial

BACKGROUND

The evidence for recommendations regarding vaccination in solid organ transplant recipients is sparse. There is little data comparing vaccine responses between groups on different immunosuppressive drugs. This study was conducted to evaluate the antibody response to Dukoral® oral cholera vaccine in renal transplant recipients (RTR).

METHODS

In a single-center non-randomized controlled clinical trial, healthy volunteers (n = 21) and renal transplant recipients (n = 30) were vaccinated with the oral whole cell/recombinant B subunit cholera vaccine Dukoral® (Valneva Inc., Vienna, Austria). The RTR were stratified according to their maintenance immunosuppressive therapy: either prednisone and a calcineurin inhibitor (cyclosporine A or tacrolimus; P/CNI group; n = 15) or prednisone and mycophenolate (P/MMF group; n = 15). All volunteers ingested Dukoral® at baseline and at day 14. Serum samples were drawn at day 0 and day 21. The primary outcome was seroconversion, defined as either a 3-fold IgA serum titer increase in anti-cholera toxin B antibodies and/or a 4-fold rise in the serum vibriocidal titer.

RESULTS

Follow-up was complete. Seroconversion after vaccination was 57% (standard error, SE 9%) in RTR and 81% (SE 9%) in healthy controls (Relative Risk, RR 0.70; 95% CI 0.48-1.02). When stratified according to maintenance immunosuppression, the seroconversion rate was 67% (SE 12%) in the P/CNI group (RR compared with controls 0.82; 95% CI 0.55-1.25) and 47% (SE 13%) in the P/MMF group (RR compared with controls 0.58; 95% CI 0.32-1.03).

CONCLUSION

Adverse events were mild to moderate and transient. The response to Dukoral was weaker and the seroconversion rate was lower in renal transplant recipients than in healthy controls. In particular, those using mycophenolate had a poor response. Nevertheless, more than half of the transplant recipients seroconverted. Therefore oral vaccines should not be discarded as a potential tool for protection of solid organ transplant recipients. This trial is registered in clinicaltrials.gov under NCT01109914.

Oral cholera vaccination strategy: Self-administration of the second dose in urban Dhaka, Bangladesh

Cholera remains a major public health problem in many developing countries including Bangladesh. The oral cholera vaccine (OCV) is now considered a key component of the public health response to cholera. Although maintaining cold chain and organizing human resource are the major challenges of vaccine delivery to the community. Here we applied an innovative approach to second dose OCV delivery to minimize financial and logistic burdens. The purpose of this study was to assess the feasibility and compliance of second dose self-administration when the second dose was provided in a plastic bag to first dose vaccine recipients as OCV is stable for up to 42 days at ambient temperatures. We aimed to deploy vaccines (N = 112,000) left over from other studies to 56,000 people aged ≥ one year living in Mirpur, Dhaka to see the feasibility of self-administration strategy. During vaccination, the first OCV dose (OCV1) was given from fixed sites and the second dose (OCV2) was provided in a plastic zip-lock bag for the participant to take the vaccine two weeks later at home. Participants were instructed to keep the vaccine away from light and in a dry cool place. Empty vials were collected following the end date of the scheduled second vaccination. Of the targeted population, 41,694 (74%) received the first OCV dose whereas an estimated 38,852 (93% of those receiving the first dose) received the second dose which represents a 7% drop out rate from OCV1 to OCV2. However the average two dose coverage was 69%. A survey of a subsample 2990 (from 8551) randomly selected households revealed that almost all respondents (98.75%) appreciated this new self-administration strategy and considered the strategy to be more practical and convenient than the usual method. This simplified, self-administered delivery strategy provides an ideal alternative for second-dose OCV delivery in hard-to-reach populations and resource-poor settings.

A randomized, observer-blinded, equivalence trial comparing two variations of Euvichol®, a bivalent killed whole-cell oral cholera vaccine, in healthy adults and children in the Philippines

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Bridging study demonstrating the equivalence of two variations of Euvichol®.

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The 600L thimerosal-free Euvichol® is safe and immunogenic in adults and children.

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The scale-up of Euvichol® allows expanding global access to oral cholera vaccine.

Background

To contribute to the global demand for oral cholera vaccine (OCV), the production of Euvichol® was scaled up with elimination of thimerosal. To demonstrate the equivalence of the variations, a study was carried out in the Philippines.

Methods

Healthy male and female adults and children in Manila were randomized to receive two doses of Euvichol® two weeks apart from either the 100L (Comparator) or the 600L (Test) variation. Primary and secondary immunogenicity endpoints were respectively geometric mean titer (GMT) of vibriocidal antibodies (two weeks post second dose) and seroconversion rate (two weeks after each dose) against O1 Inaba, Ogawa, and O139 serogroups. The GMT of vibriocidal antibodies against O1 Inaba, Ogawa, and O139 two weeks post first dose was also measured. To show the equivalence of two variations of Euvichol®, the ratio of GMT and the difference of seroconversion rate between Test and Comparator vaccines were tested with equivalence margin of [0.5, 2.0] for GMT ratio and of 15% for seroconversion rate, respectively. Safety assessment included solicited reactogenicity within 6 days after each dose and unsolicited and serious adverse events.

Results

A total of 442 participants were enrolled. For the overall population, equivalence between Test and Comparator was demonstrated for vibriocidal antibody response against O1 Inaba and Ogawa serotypes and O139 serogroup in both modified intention-to-treat (mITT) and per protocol analysis, since the 95% confidence intervals (CI) of GMT to any serotypes were within the lower and upper boundary [0.5, 2.0]. Seroconversion rates after two doses also showed equivalence for O1 Inaba, Ogawa, and O139. The vaccine was safe and well tolerated, similarly between the two groups.

Conclusion

The study results support the equivalence of the 600L Euvichol® to the 100L formulation in healthy children and adults. The 600L Euvichol® is safe and immunogenic in adults and children.

ClinicalTrials.gov registration number: NCT02502331.

Socioeconomic drivers of vaccine uptake: An analysis of the data of a geographically defined cluster randomized cholera vaccine trial in Bangladesh

BACKGROUND

Evaluations of oral cholera vaccines (OCVs) have demonstrated their effectiveness in diverse settings. However, low vaccine uptake in some settings reduces the opportunity for prevention. This paper identifies the socioeconomic factors associated with vaccine uptake in a mass vaccination program.

METHODS

This was a three-arm (vaccine, vaccine plus behavioral change, and non-intervention) cluster randomized trial conducted in Dhaka, Bangladesh. Socio-demographic and vaccination data were collected from 268,896 participants. A geographical information system (GIS) was used to design and implement the vaccination program. A logistic regression model was used to assess the association between vaccine uptake and socioeconomic characteristics.

RESULTS

The GIS supported the implementation of the vaccination program by identifying ideal locations of vaccination centres for equitable population access, defining catchment areas of daily activities, and providing daily coverage maps during the campaign. Among 188,206 individuals in the intervention arms, 123,686 (66%) received two complete doses, and 64,520 (34%) received one or no doses of the OCV. The vaccine uptake rate was higher in females than males (aOR: 1.80; 95% CI = 1.75-1.84) and in younger (<15 years) than older participants (aOR: 2.19; 95% CI = 2.13-3.26). Individuals living in their own house or having a higher monthly family expenditure were more likely to receive the OCV (aOR: 1.60; 95% CI = 1.50-1.70 and aOR: 1.14; 95% CI = 1.10-1.18 respectively). Individuals using treated water for drinking or using own tap as the source of water were more likely to receive the OCV (aOR: 1.23; 95% CI = 1.17-1.29 and aOR: 1.14; 95% CI = 1.02-1.25 respectively) than their counterpart. Vaccine uptake was also significantly higher in participants residing farther away from health facilities (aOR: 95% 1.80; CI = 1.36-2.37).

CONCLUSION

The GIS was useful in designing field activities, facilitating vaccine delivery and identifying socioeconomic drivers of vaccine uptake in the urban area of Bangladesh. Addressing these socioeconomic drivers may help improve OCV uptake, thereby effectiveness of the OCV in a community.

Use of oral cholera vaccine as a vaccine probe to define the geographical dimensions of person-to-person transmission of cholera

Background

Cholera is known to be transmitted from person to person, and inactivated oral cholera vaccines (OCVs) have been shown to confer herd protection via interruption of this transmission. However, the geographic dimensions of chains of person-to-person transmission of cholera are uncertain. The ability of OCVs to confer herd protection was used to define these dimensions in two cholera-endemic settings, one in rural Bangladesh and the other in urban India.

Methods

Two large randomized, placebo-controlled trials of inactivated OCVs, one in rural Matlab, Bangladesh and the other in urban Kolkata, India, were reanalyzed. Vaccine herd protection was evaluated by relating the risk of cholera in placebo recipients to vaccine coverage of surrounding residents residing within concentric rings. In Matlab, concentric rings in 100-m increments up to 700 m were evaluated; in Kolkata, 50-m increments up to 350m were evaluated.

Results

One hundred and eight cholera cases among 24 667 placebo recipients were detected during 1 year of post-vaccination follow-up at Matlab; 128 cholera cases among 34 968 placebo recipients were detected during 3 years of follow-up in Kolkata. Consistent inverse relationships were observed between vaccine coverage of the ring and the risk of cholera in the central placebo recipient for rings with radii up to 500 m in Matlab and up to 150 m in Kolkata.

Conclusions

These results suggest that the dimensions of chains of person-to-person transmission in endemic settings can be quite large and may differ substantially from setting to setting. Using OCVs as 'probes' to define these dimensions can inform geographical targeting strategies for the deployment of these vaccines in endemic settings.

Socioeconomic risk factors for cholera in different transmission settings: An analysis of the data of a cluster randomized trial in Bangladesh

BACKGROUND

Cholera remains a threat globally, and socioeconomic factors play an important role in transmission of the disease. We assessed socioeconomic risk factors for cholera in vaccinated and non-vaccinated communities to understand whether the socioeconomic risk factors differ by transmission patterns for cholera.

METHODS

We used data from a cluster randomized control trial conducted in Dhaka, Bangladesh. There were 90 geographic clusters; 30 in each of the three arms of the study: vaccine (VAC), vaccine plus behavioural change (VBC), and non-intervention. The data were analysed for the three populations: (1) vaccinees in the vaccinated communities (VAC and VBC arms), (2) non-vaccinated individuals in the vaccinated communities and (3) all individuals in the non-vaccinated communities (non-intervention arm). A generalized estimating equation with logit link function was used to evaluate the risk factors for cholera among these different populations adjusting for household level correlation in the data.

RESULTS

A total of 528 cholera and 226 cholera with severe dehydration (CSD) in 268,896 persons were observed during the two-year follow-up. For population 1, the cholera risk was not associated with any socioeconomic factors; however CSD was less likely to occur among individuals living in a household having ≤4 members (aOR=0.55, 95% CI=0.32-0.96). Among population 2, younger participants and individuals reporting diarrhoea during registration were more likely to have cholera. Females and individuals reporting diarrhoea during registration were at increased risk of CSD. Among population 3, individuals living in a household without a concrete floor, in an area with high population density, closer to the study hospital, or not treating drinking water were at significantly higher risk for both cholera and CSD.

CONCLUSION

The profile of socioeconomic factors associated with cholera varies by individuals' vaccination status as well as the transmission setting. In a vaccinated community where transmission would be expected to be lower, socioeconomic factors may not increase the risk of the disease.

Oral cholera vaccine coverage in hard-to-reach fishermen communities after two mass Campaigns, Malawi, 2016

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Simplified delivery strategies were proposed in hard-to-reach population.

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High full coverage was reached in the most at-risk individuals.

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Vaccines use efficiency need to be improved.

Context

From December 2015 to August 2016, a large epidemic of cholera affected the fishermen of Lake Chilwa in Malawi. A first reactive Oral Cholera Vaccines (OCV) campaign was organized, in February, in a 2 km radius of the lake followed by a preemptive one, conducted in November, in a 25 km radius. We present the vaccine coverage reached in hard-to-reach population using simplified delivery strategies.

Method

We conducted two-stage random-sampling cross-sectional surveys among individuals living in a 2 km and 25 km radius of Lake Chilwa (islands and floating homes included). Individuals aged 12 months and older from Machinga and Zomba districts were sampled: 43 clusters of 14 households were surveyed. Simplified strategies were used for those living in islands and floating homes: self- delivery and community-supervised delivery of the second dose. Vaccine coverage (VC) for at-least-two-doses was estimated taking into account sampling weights and design effects.

Results

A total of 1176 households were surveyed (2.7% of non-response). Among the 2833 individuals living in the 2 km radius of Lake and the 2915 in the 25 km radius: 457 (16.1%) and 239 (8.2%) lived in floating homes or on islands at some point in the year, respectively. For the overall population, VC was 75.6% and 54.2%, respectively. In the 2 km radius, VC was 92.2% for those living on the lake at some point of the year: 271 (64.8%) used the simplified strategies. The main reasons for non-vaccination were absence during the campaign and vaccine shortage. Few adverse events occurring in the 24 h following vaccination was reported.

Conclusions

We reached a high two-dose coverage of the most at-risk population using simplified delivery strategies. Because of the high fishermen mobility, regular catch-up campaigns or another strategy specifically targeting fishermen need to be assessed for more efficient vaccines use.

Safety of the oral cholera vaccine in pregnancy: Retrospective findings from a subgroup following mass vaccination campaign in Dhaka, Bangladesh

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Few women received the OCV unknowingly while pregnant during a large vaccine trial.

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There is limited data on the safety of OCVs in pregnancy.

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We evaluated the effect of a killed OCV, Shanchol™, on pregnancy outcomes.

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Study showed no evidence of exposure to Shanchol™ on adverse pregnancy outcomes.

Background

Pregnant women are vulnerable to complications of cholera. Killed oral cholera vaccines (OCV) are not recommended for pregnant women though there is no evidence of harmful effects during pregnancy. We evaluated the effect of a killed OCV, Shanchol™, on pregnancy outcomes during an effectiveness trial of the vaccine in urban Bangladesh.

Methodology

Individuals ⩾1 year were invited to participate in the trial, conducted in 2011 in Dhaka, Bangladesh. Pregnancy by history was an exclusion criterion and all women of reproductive age (15–49 years) were verbally questioned about pregnancy at enrollment and prior to vaccination. Out of 48,414 women of reproductive age 286 women received the OCV unknowingly while pregnant. Out of these, we could recruit 69 women defined as exposed to OCV. Accordingly, we selected 69 pregnant women randomly from those who did not take the OCV (non-exposed to OCV). We evaluated adverse pregnancy outcome (spontaneous miscarriages, still births, or congenital malformations) between those who were exposed to OCV and those who were not exposed to OCV.

Results

About 16% of pregnant women exposed to OCV had pregnancy loss, as compared to 12% of unvaccinated pregnant women (P = 0.38). One congenital anomaly was observed and occurred in women non-exposed to OCV group. Models that adjusted for baseline characteristics that were unbalanced between the exposed and non-exposed groups, revealed a no elevation of risk of adverse pregnancy outcomes in vaccinees versus non-vaccinees (Adj. OR (95% CI): 0.45 (0.11–1.88).

Conclusions

No excess of adverse fetal outcomes associated with receipt of OCV was observed in this study.

Trial registration: Clinical Trials.gov number NCT01339845.

The oral cholera vaccine Shanchol™ when stored at elevated temperatures maintains the safety and immunogenicity profile in Bangladeshi participants

BACKGROUND

The oral cholera vaccine (OCV), Shanchol™ has shown protective efficacy lasting up to 5 years, however, requirement for a cold chain limits its use in resource poor settings. The study was conducted to determine the safety and immunogenicity of Shanchol in adult participants in Bangladesh when stored at elevated temperatures.

METHODS

The study was conducted in Mirpur, Dhaka. Four groups of healthy adult participants received two doses of Shanchol™, kept under standard storage temperature (Group A; 2-8°C) or at elevated temperatures (Group B, 25°C; Group C, 37°C; Group D, 42°C) for 14 days, respectively. Vaccine specific antibody responses were determined.

FINDINGS

145 participants were assigned to each group. Adverse events were mild not differing among groups. Vaccine stored at elevated temperatures remained stable with cumulative LPS content within admissible limits. Vibriocidal antibody responses were observed in all groups after each dose of vaccine at day 7 and 21 compared to pre-immune levels (P<0.001). Four-fold increases to Vibrio cholerae O1 Ogawa were observed at day 7 and/or day 21 after vaccination in the standard temperature and the three elevated temperature groups, with responder rates of; 76% (95% CI LB; 70%), 80% (95% CI LB; 74%), 69% (95% CI LB; 63%), and 74% (95% CI LB; 68%) in Groups A-D, respectively (P=0.240). Responses were also seen in all groups to V. cholerae O1 Inaba and V. cholerae O139 and in LPS specific IgA response to V. cholerae O1 antigens.

INTERPRETATION

This is the first report to show that the OCV is stable at elevated temperatures, and the safety and immunogenicity profiles are not altered. This information will help formulate global policies for use of the vaccine at higher temperatures, resulting in easier distribution and vaccination costs and decrease logistical challenges to vaccine delivery.

FUNDING

Bill & Melinda Gates Foundation.

TRIAL REGISTRATION

Clinical Trials.gov number NCT01762930.

A randomized, non-inferiority trial comparing two bivalent killed, whole cell, oral cholera vaccines (Euvichol vs Shanchol) in the Philippines

BACKGROUND

Currently, there are two oral cholera vaccines (OCV) that are prequalified by the World Health Organization. Both (Dukoral and Shanchol) have been proven to be safe, immunogenic, and effective. As the global supply of OCV remains limited, we assessed the safety and immunogenicity of a new low cost, killed, bivalent OCV (Euvichol) in the Philippines.

METHODS

The randomized controlled trial was carried out in healthy Filipino adults and children. Two doses of either the current WHO prequalified OCV (Shanchol) or the same composition OCV being considered for WHO prequalification (Euvichol) were administered to participants.

RESULTS

The pivotal study was conducted in total of 1263 healthy participants (777 adults and 486 children). No serious adverse reactions were elicited in either vaccine groups. Vibriocidal antibody responses to V. cholerae O1 Inaba following administration of two doses of Euvichol were non-inferior to those of Shanchol in adults (82% vs 76%) and children (87% vs 89%). Similar findings were observed for O1 Ogawa in adults (80% vs 74%) and children (91% vs 88%).

CONCLUSION

A two dose schedule with Euvichol induces a strong vibriocidal response comparable to those elicited by the currently WHO prequalified OCV, Shanchol. Euvichol will be an oral cholera vaccine suitable for use in lower income countries, where cholera still has a significant economic and public health impact.

Peru-15 (Choleragarde(®)), a live attenuated oral cholera vaccine, is safe and immunogenic in human immunodeficiency virus (HIV)-seropositive adults in Thailand

BACKGROUND

Many areas with endemic and epidemic cholera report significant levels of HIV transmission. According to the World Health Organization (WHO), over 95% of reported cholera cases occur in Africa, which also accounts for nearly 70% of people living with HIV/AIDS globally. Peru-15, a promising single dose live attenuated oral cholera vaccine (LA-OCV), was previously found to be safe and immunogenic in cholera endemic areas. However, no data on the vaccine's safety among HIV-seropositive adults had been collected.

METHODS

This study was a double-blinded, individually randomized, placebo-controlled trial enrolling HIV-seropositive adults, 18-45 years of age, conducted in Bangkok, Thailand, to assess the safety of Peru-15 in a HIV-seropositive cohort.

RESULTS

32 HIV infected subjects were randomized to receive either a single oral dose of the Peru-15 vaccine with a buffer or a placebo (buffer only). No serious adverse events were reported during the follow-up period in either group. The geometric mean fold (GMF) rise in V. cholerae O1 El Tor specific antibody titers between baseline and 7 days after dosing was 32.0 (p<0.001) in the vaccine group compared to 1.6 (p<0.14) in the placebo group. Among the 16 vaccinees,14 vaccinees (87.5%) had seroconversion compared to 1 of 16 placebo recipients (6.3%). V. cholerae was isolated from the stool of one vaccinee, and found to be genetically identical to the Peru-15 vaccine strain. There were no significant changes in HIV viral load or CD4 T-cell counts between vaccine and placebo groups.

CONCLUSION

Peru-15 was shown to be safe and immunogenic in HIV-seropositive Thai adults.

Feasibility of a preventive mass vaccination campaign with two doses of oral cholera vaccine during a humanitarian emergency in South Sudan

BACKGROUND

As an adjunct to cholera prevention measures, WHO advises the use of oral cholera vaccine through mass vaccination campaigns in high-risk areas and for vulnerable population groups. We assessed the feasibility and acceptability of a mass vaccination campaign using 1) a predominantly fixed and 2) a mobile door-to-door strategy.

METHODS

Vaccination included administration of two doses (given 2 weeks apart) of oral cholera vaccine to individuals older than 1 year of age, in four refugee camps: Jamam, Doro, Batil and Gendrassa, and the host population in Maban County, South Sudan, from December 2012 to February 2013.

RESULTS

A total of 258 832 doses were administered to a population of 166 000 (126 000 refugees and 40 000 host population). The first round coverage for the refugees was above 84% for Doro, Jamam and Batil and 104% for Gendrassa. The second dose reached the same coverage as the first dose. For the host population, the coverage for the first dose was above 90% in Doro and Jamam and 53% in Gendrassa and Batil. For the second round, the coverage was above 79% in Doro and Jamam and above 70% in Batil and Gendrassa.

CONCLUSIONS

The vaccination of a large population in an emergency context proved to be feasible and acceptable and achieved high coverage. This is encouraging and is a way forward for reducing cholera related morbidity and mortality among vulnerable populations.

A 6-week oral toxicity study of oral cholera vaccine in sprague-dawley rats

The present study was carried out to examine the toxicity and target organs of oral cholera vaccine (OCV) after repeated oral administration in Sprague-Dawley rats for 6 weeks (3 administrations, once every 2 weeks). OCV is an inactivated oral cholera vaccine that contains Vibrio cholerae and confers protection against cholera caused by V. cholera serogroups O1 (Inaba and Ogawa serotypes) and O139 (strain 4260B). The animals were orally administered either OCV placebo (negative control) or OCV at a dose equivalent to 240 times the anticipated human dose. Throughout the administration period, no significant change was detected in clinical signs, body weight, food or water consumption, urinalysis results, hematological and clinical biochemistry test results, organ weights, necropsy, or histopathological examination results. Minor changes were found in hematological and clinical biochemistry tests; however, these changes were within normal ranges. The above results suggest that oral administration of OCV in rats did not induce any toxicologically meaningful changes, and the target organs could not be determined. This study was conducted in accordance with the guidelines established by Good Laboratory Practice (2009-183, KFDA, December 22, 2009) and the OECD Principles of Good Laboratory Practice (1997).