Safety and immunogenicity of a live oral recombinant cholera vaccine VA1.4: a randomized, placebo controlled trial in healthy adults in a cholera endemic area in Kolkata, India

BACKGROUND

A live oral cholera vaccine VA 1.4 developed from a non-toxigenic Vibrio cholerae O1 El Tor strain using ctxB gene insertion was further developed into a clinical product following cGMP and was evaluated in a double-blind randomized placebo controlled parallel group two arm trial with allocation ratio of 1∶1 for safety and immunogenicity in men and women aged 18-60 years from Kolkata, India.

METHOD

A lyophilized dose of 1.9×109 CFU (n = 44) or a placebo (n = 43) reconstituted with a diluent was administered within 5 minutes of drinking 100 ml of a buffer solution made of sodium bicarbonate and ascorbic acid and a second dose on day 14.

RESULT

The vaccine did not elicit any diarrhea related adverse events. Other adverse events were rare, mild and similar in two groups. One subject in the vaccine group excreted the vaccine strain on the second day after first dose. The proportion of participants who seroconverted (i.e. had 4-folds or higher rise in reciprocal titre) in the vaccine group were 65.9% (95% CI: 50.1%-79.5%) at both 7 days (i.e. after 1st dose) and 21 days (i.e. after 2nd dose). None of the placebo recipients seroconverted. Anti-cholera toxin antibody was detected in very few recipients of the vaccine.

CONCLUSION

This study demonstrates that VA 1.4 at a single dose of 1.9×109 is safe and immunogenic in adults from a cholera endemic region. No additional benefit after two doses was seen.

TRIAL REGISTRATION

Clinical Trials Registry-India, National Institute of Medical Statistics (Indian Council of Medical Research) CTRI/2012/04/002582.

Vibriocidal antibody responses to a bivalent killed whole-cell oral cholera vaccine in a phase III trial in Kolkata, India

BACKGROUND

During the development of a vaccine, identification of the correlates of protection is of paramount importance for establishing an objective criterion for the protective performance of the vaccine. However, the ascertainment of correlates of immunity conferred by any vaccine is a difficult task.

METHODS

While conducting a phase three double-blind, cluster-randomized, placebo-controlled trial of a bivalent killed whole-cell oral cholera vaccine in Kolkata, we evaluated the immunogenicity of the vaccine in a subset of participants. Randomly chosen participants (recipients of vaccine or placebo) were invited to provide blood samples at baseline, 14 days after the second dose and one year after the first dose. At these time points, serum geometric mean titers (GMT) of vibriocidal antibodies and seroconversion rates for vaccine and placebo arms were calculated and compared across the age strata (1 to 5 years, 5 to 15 years and more than 15 years) as well as for all age groups.

RESULTS

Out of 137 subjects included in analysis, 69 were vaccinees and 68 received placebo. There were 5•7 and 5•8 geometric mean fold (GMF) rises in titers to Vibrio cholerae Inaba and Ogawa, respectively at 14 days after the second dose, with 57% and 61% of vaccinees showing a four-fold or greater titer rise, respectively. After one year, the titers to Inaba and Ogawa remained 1•7 and 2•8 fold higher, respectively, compared to baseline. Serum vibriocidal antibody response to V. cholerae O139 was much lower than that to Inaba or Ogawa. No significant differences in the GMF-rises were observed among the age groups.

CONCLUSIONS

The reformulated oral cholera vaccine induced a statistically significant anti-O1 Inaba and O1 Ogawa vibriocidal antibody response 14 days after vaccination, which although declined after one year remained significantly higher than baseline. Despite this decline, the vaccine remained protective five years after vaccination.

Immunogenicity of a killed bivalent (O1 and O139) whole cell oral cholera vaccine, Shanchol, in Haiti

Background

Studies of the immunogenicity of the killed bivalent whole cell oral cholera vaccine, Shanchol, have been performed in historically cholera-endemic areas of Asia. There is a need to assess the immunogenicity of the vaccine in Haiti and other populations without historical exposure to Vibrio cholerae.

Methodology/Principal Findings

We measured immune responses after administration of Shanchol, in 25 adults, 51 older children (6–17 years), and 47 younger children (1–5 years) in Haiti, where cholera was introduced in 2010. A≥4-fold increase in vibriocidal antibody titer against V. cholerae O1 Ogawa was observed in 91% of adults, 74% of older children, and 73% of younger children after two doses of Shanchol; similar responses were observed against the Inaba serotype. A≥2-fold increase in serum O-antigen specific polysaccharide IgA antibody levels against V. cholerae O1 Ogawa was observed in 59% of adults, 45% of older children, and 61% of younger children; similar responses were observed against the Inaba serotype. We compared immune responses in Haitian individuals with age- and blood group-matched individuals from Bangladesh, a historically cholera-endemic area. The geometric mean vibriocidal titers after the first dose of vaccine were lower in Haitian than in Bangladeshi vaccinees. However, the mean vibriocidal titers did not differ between the two groups after the second dose of the vaccine.

Conclusions/Significance

A killed bivalent whole cell oral cholera vaccine, Shanchol, is highly immunogenic in Haitian adults and children. A two-dose regimen may be important in Haiti, and other populations lacking previous repeated exposures to V. cholerae.

Studies evaluating the ability of the killed bivalent whole cell oral cholera vaccine, Shanchol, to elicit an immune response have been performed in historically cholera-endemic areas of Asia. There is a need to assess whether the vaccine is able to elicit an immune response in Haiti and other populations without historical exposure to cholera. In this study, we measure immune responses after administration of Shanchol, in 25 adults, 51 older children (6–17 years), and 47 younger children (1–5 years) in Haiti, where cholera was introduced in 2010. A killed bivalent whole cell oral cholera vaccine (Shanchol) is capable of inducing an immune response in adults and children living in Haiti. However, a two-dose regimen may be important in Haiti and other populations lacking historical exposure to cholera.

Safety and immunogenicity assessment of an oral cholera vaccine through phase I clinical trial in Korea

The safety, tolerability and immunogenicity of an oral cholera vaccine (OCV) was assessed in adult Korean male through an open-label, non-comparative clinical study. Two doses of vaccine with an interval of 2 weeks were given to 20 healthy subjects. A total of 7 adverse events occurred in 6 subjects. However, no clinically significant change was observed in electrocardiograms, vital signs, physical examinations, and clinical laboratory tests. The immunogenicity of OCV was evaluated by serum vibriocidal assay where anti-Vibrio cholerae O1 and O139 antibodies were measured at day 0, 14, and 28 of vaccine administration. The antibody titers ranged from < 2.5-5,120 for V. cholerae O1 Inaba, < 2.5-10,240 for V. cholerae O1 Ogawa and < 2.5-480 for V. cholerae O139. In addition, the fold increase in antibody titers ranged from 1-4,096 for O1 Inaba, 1-8,192 for O1 Ogawa, and 1-384 for O139. The seroconversion rate was 95% and 45% for O1 and O139 antibodies, respectively. Our study clearly shows that administration of two doses of OCV at a 2 week-interval increases an appropriate level of antibody titer in the serum of healthy Korean adult males (Clinical Trial Number, NCT01707537).

Evaluation in mice of a conjugate vaccine for cholera made from Vibrio cholerae O1 (Ogawa) O-specific polysaccharide

Background

Protective immunity against cholera is serogroup specific. Serogroup specificity in Vibrio cholerae is determined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). Generally, polysaccharides are poorly immunogenic, especially in young children.

Methodology

Here we report the evaluation in mice of a conjugate vaccine for cholera (OSP:TThc) made from V. cholerae O1 Ogawa O-Specific Polysaccharide–core (OSP) and recombinant tetanus toxoid heavy chain fragment (TThc). We immunized mice intramuscularly on days 0, 21, and 42 with OSP:TThc or OSP only, with or without dmLT, a non-toxigenic immunoadjuvant derived from heat labile toxin of Escherichia coli.

Principal Findings

We detected significant serum IgG antibody responses targeting OSP following a single immunization in mice receiving OSP:TThc with or without adjuvant. Anti-LPS IgG responses were detected following a second immunization in these cohorts. No anti-OSP or anti-LPS IgG responses were detected at any time in animals receiving un-conjugated OSP with or without immunoadjuvant, and in animals receiving immunoadjuvant alone. Responses were highest following immunization with adjuvant. Serum anti-OSP IgM responses were detected in mice receiving OSP:TThc with or without immunoadjuvant, and in mice receiving unconjugated OSP. Serum anti-LPS IgM and vibriocidal responses were detected in all vaccine cohorts except in mice receiving immunoadjuvant alone. No significant IgA anti-OSP or anti-LPS responses developed in any group. Administration of OSP:TThc and adjuvant also induced memory B cell responses targeting OSP and resulted in 95% protective efficacy in a mouse lethality cholera challenge model.

Conclusion

We describe a protectively immunogenic cholera conjugate in mice. Development of a cholera conjugate vaccine could assist in inducing long-term protective immunity, especially in young children who respond poorly to polysaccharide antigens.

Cholera is a severe dehydrating diarrheal illness of humans caused by organisms Vibrio cholerae serogroups O1 or O139 serogroup organisms. Protective immunity against cholera is serogroup specific. Serogroup specificity in V. cholerae is determined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). Generally, polysaccharides are poorly immunogenic, especially in young children. Unfortunately, children bear a large burden of cholera globally. Here we describe a novel cholera conjugate vaccine and show that it induces immune responses in mice, including memory responses, to OSP, the T cell-independent antigen that probably is the target of protective immunity to cholera. These responses were highest following immunization of the vaccine with a novel immunoadjuvant, dmLT. We also show that immunization of mice with this conjugate vaccine protects against challenge with wild-type V. cholerae. A protectively immunogenic cholera conjugate vaccine that induces long-term memory responses could have particular utility in young children who are most at risk of cholera.

Construction and evaluation of V. cholerae O139 mutant, VCUSM21P, as a safe live attenuated cholera vaccine

Cholera is a major infectious disease, affecting millions of lives annually. In endemic areas, implementation of vaccination strategy against cholera is vital. As the use of safer live vaccine that can induce protective immunity against Vibrio cholerae O139 infection is a promising approach for immunization, we have designed VCUSM21P, an oral cholera vaccine candidate, which has ctxA that encodes A subunit of ctx and mutated rtxA/C, ace and zot mutations. VCUSM21P was found not to disassemble the actin of HEp2 cells. It colonized the mice intestine approximately 1 log lower than that of the Wild Type (WT) strain obtained from Hospital Universiti Sains Malaysia. In the ileal loop assay, unlike WT challenge, 1×10⁶ and 1×10⁸ colony forming unit (CFU) of VCUSM21P was not reactogenic in non-immunized rabbits. Whereas, the reactogenicity caused by the WT in rabbits immunized with 1×10¹⁰ CFU of VCUSM21P was found to be reduced as evidenced by absence of fluid in loops administered with 1×10²–1×10⁷ CFU of WT. Oral immunization using 1×10¹⁰ CFU of VCUSM21P induced both IgA and IgG against Cholera Toxin (CT) and O139 lipopolysaccharides (LPS). The serum vibriocidal antibody titer had a peak rise of 2560 fold on week 4. Following Removable Intestinal Tie Adult Rabbit Diarrhoea (RITARD) experiment, the non-immunized rabbits were found not to be protected against lethal challenge with 1×10⁹ CFU WT, but 100% of immunized rabbits survived the challenge. In the past eleven years, V. cholerae O139 induced cholera has not been observed. However, attenuated VCUSM21P vaccine could be used for vaccination program against potentially fatal endemic or emerging cholera caused by V. cholerae O139.

Age-dependent association among Helicobacter pylori infection, serum pepsinogen levels and immune response of children to live oral cholera vaccine CVD 103-HgR

Background

Through its effects on gastric secretion, we hypothesized that Helicobacter pylori infection may influence oral immunization. Accordingly, we examined the association between H. pylori infection, serum pepsinogen (PG) (measures for H. pylori gastritis) and vibriocidal antibody (a correlate of protection) seroconversion following oral immunization with CVD 103-HgR live cholera vaccine among children of different ages.

Methods

Sera from 422 Chilean children who were vaccinated with a single dose of CVD 103-HgR were tested by ELISA for serum IgG antibodies to H. pylori, PG I and PG II levels and antibodies to Shigella flexneri 2a lipopolysaccharide and hepatitis A virus (as markers of low socioeconomic status and exposure to enteric pathogens).

Results

The likelihood of vibriocidal antibody seroconversion following vaccination with CVD 103-HgR was significantly decreased in H. pylori-seropositive children age 6 months to 4 years with PG II>8 µg/L (adjusted OR 0.14 (95% CI 0.03–0.61; P = 0.009), and also in H. pylori seropositives with lower PG II level (adjusted OR 0.34, 95% CI 0.14–0.83; P = 0.017), compared to H. pylori-seronegatives. H. pylori-seropositive children aged 5–9 years with serum PG I>30 µg/L (indicating more severe gastritis) had higher odds of vibriocidal seroconversion than those with lower PG I levels (adjusted OR 4.41, 95%CI 1.26–15.38; P = 0.02). There was no significant association between exposures to S. flexneri 2a or hepatitis A virus and vibriocidal seroconversion.

Conclusions

As H. pylori gastritis progresses with increasing pediatric age in developing country venues, changes in gastric secretion ensue that we believe explain the observed differences in age-related immune responses to immunization with live oral cholera vaccine. The effect of H. pylori and changes of gastric acid secretion on the immunogenicity of various oral vaccines should be studied in different developing, transitional and industrialized country settings.

Use of oral cholera vaccine in Haiti: a rural demonstration project

A cholera epidemic has claimed the lives of more than 8,000 Haitians and sickened 650,000 since the outbreak began in October 2010. Early intervention in the epidemic focused on case-finding, treatment, and water and sanitation interventions for prevention of transmission. Use of oral cholera vaccine (OCV) as part of a complementary set of control activities was considered but initially rejected by policymakers. In December 2011, the Minister of Health of Haiti called for a demonstration of the acceptability and feasibility of the use of OCV in urban and rural Haiti. This paper describes the collaborative activity that offered OCV to one region of the Artibonite Department of rural Haiti in addition to other ongoing treatment and control measures. Despite logistics and cold chain challenges, 45,417 persons were successfully vaccinated with OCV in the region, and 90.8% of these persons completed their second dose.

Development of a cholera vaccination policy on the Island of Hispaniola, 2010-2013

Deployment of oral cholera vaccine (OCV) on the Island of Hispaniola has been considered since the emergence of the disease in October of 2010. At that time, emergency response focused on the time-tested measures of treatment to prevent deaths and sanitation to diminish transmission. Use of the limited amount of vaccine available in the global market was recommended for demonstration activities, which were carried out in 2012. As transmission continues, vaccination was recommended in Haiti as one component of a comprehensive initiative supported by an international coalition to eliminate cholera on the Island of Hispaniola. Leveraging its delivery to strengthen other cholera prevention measures and immunization services, a phased OCV introduction is pursued in accordance with global vaccine supply. Not mutually exclusive or sequential deployment options include routine immunization for children over the age of 1 year and campaigns in vulnerable metropolitan areas or rural areas with limited access to health services.

Cholera vaccination in urban Haiti

Successful and sustained efforts have been made to curtail the major cholera epidemic that occurred in Haiti in 2010 with the promotion of hygiene and sanitation measures, training of health personnel and establishment of treatment centers nationwide. Oral cholera vaccine (OCV) was introduced by the Haitian Ministry of Health as a pilot project in urban and rural areas. This paper reports the successful OCV pilot project led by GHESKIO Centers in the urban slums of Port-au-Prince where 52,357 persons received dose 1 and 90.8% received dose 2; estimated coverage of the at-risk community was 75%. This pilot study demonstrated the effort, community mobilization, and organizational capacity necessary to achieve these results in a challenging setting. The OCV intervention paved the way for the recent launching of a national cholera vaccination program integrated in a long-term ambitious and comprehensive plan to address Haiti's critical need in water security and sanitation.

Cholera vaccination campaign contributes to improved knowledge regarding cholera and improved practice relevant to waterborne disease in rural Haiti

Background

Haiti's cholera epidemic has been devastating partly due to underlying weak infrastructure and limited clean water and sanitation. A comprehensive approach to cholera control is crucial, yet some have argued that oral cholera vaccination (OCV) might result in reduced hygiene practice among recipients. We evaluated the impact of an OCV campaign on knowledge and health practice in rural Haiti.

Methodology/Principal Findings

We administered baseline surveys on knowledge and practice relevant to cholera and waterborne disease to every 10th household during a census in rural Haiti in February 2012 (N = 811). An OCV campaign occurred from May–June 2012 after which we administered identical surveys to 518 households randomly chosen from the same region in September 2012. We compared responses pre- and post-OCV campaign.

Post-vaccination, there was improved knowledge with significant increase in percentage of respondents with ≥3 correct responses on cholera transmission mechanisms (odds ratio[OR] 1.91; 95% confidence interval[CI] 1.52–2.40), preventive methods (OR 1.83; 95% CI 1.46–2.30), and water treatment modalities (OR 2.75; 95% CI 2.16–3.50). Relative to pre-vaccination, participants were more likely post-OCV to report always treating water (OR 1.62; 95% CI 1.28–2.05). Respondents were also more likely to report hand washing with soap and water >4 times daily post-vaccine (OR 1.30; 95% CI 1.03–1.64). Knowledge of treating water as a cholera prevention measure was associated with practice of always treating water (OR 1.47; 95% CI 1.14–1.89). Post-vaccination, knowledge was associated with frequent hand washing (OR 2.47; 95% CI 1.35–4.51).

Conclusion

An OCV campaign in rural Haiti was associated with significant improvement in cholera knowledge and practices related to waterborne disease. OCV can be part of comprehensive cholera control and reinforce, not detract from, other control efforts in Haiti.

In October 2010, Haiti experienced a cholera outbreak that is now considered one of the largest cholera epidemics in recent history. A comprehensive approach is necessary to successfully fight the epidemic and proven methods for controlling cholera include improving access to clean water and sanitation as well as widespread hygiene education. In addition, there are two safe cholera vaccines approved for use. The authors conducted surveys before and after a cholera vaccination campaign, that included a public health educational component, in rural Haiti; surveys addressed knowledge of cholera and hygiene practices such as hand washing and water treatment, which are crucial for preventing waterborne diseases such as cholera. The authors found that after the vaccination campaign, knowledge of cholera improved significantly. There was also significant increase in reported hand washing and water treatment post vaccination. Furthermore, there was an association between knowledge and hygiene practices. Therefore, this study demonstrates that cholera vaccination can be a complementary tool in the fight against cholera in Haiti and will not detract from other control efforts.

The ABCs (Antibody, B Cells, and Carbohydrate Epitopes) of Cholera Immunity: Considerations for an Improved Vaccine

Cholera, a diarrheal disease, is known for explosive epidemics that can quickly kill thousands. Endemic cholera is a seasonal torment that also has a significant mortality. Not all nations with extensive rural communities can achieve the required infrastructure or behavioral changes to prevent epidemic or endemic cholera. For some communities, a single-dose cholera vaccine that protects those at risk is the most efficacious means to reduce morbidity and mortality. It is clear that our understanding of what a protective cholera immune response is has not progressed at the rate our understanding of the pathogenesis and molecular biology of cholera infection has. This review addresses V. cholerae lipopolysaccharide (LPS)-based immunogens because LPS is the only immunogen proven to induce protective antibody in humans. We discuss the role of anti-LPS antibodies in protection from cholera, the importance and the potential role of B cell subsets in protection that is based on their anatomical location and the intrinsic antigen-receptor specificity of various subsets is introduced.

First outbreak response using an oral cholera vaccine in Africa: vaccine coverage, acceptability and surveillance of adverse events, Guinea, 2012

BACKGROUND

Despite World Health Organization (WHO) prequalification of two safe and effective oral cholera vaccines (OCV), concerns about the acceptability, potential diversion of resources, cost and feasibility of implementing timely campaigns has discouraged their use. In 2012, the Ministry of Health of Guinea, with the support of Médecins Sans Frontières organized the first mass vaccination campaign using a two-dose OCV (Shanchol) as an additional control measure to respond to the on-going nationwide epidemic. Overall, 316,250 vaccines were delivered. Here, we present the results of vaccination coverage, acceptability and surveillance of adverse events.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a cross-sectional cluster survey and implemented adverse event surveillance. The study population included individuals older than 12 months, eligible for vaccination, and residing in the areas targeted for vaccination (Forécariah and Boffa, Guinea). Data sources were household interviews with verification by vaccination card and notifications of adverse events from surveillance at vaccination posts and health centres. In total 5,248 people were included in the survey, 3,993 in Boffa and 1,255 in Forécariah. Overall, 89.4% [95%CI:86.4-91.8%] and 87.7% [95%CI:84.2-90.6%] were vaccinated during the first round and 79.8% [95%CI:75.6-83.4%] and 82.9% [95%CI:76.6-87.7%] during the second round in Boffa and Forécariah respectively. The two dose vaccine coverage (including card and oral reporting) was 75.8% [95%CI: 71.2-75.9%] in Boffa and 75.9% [95%CI: 69.8-80.9%] in Forécariah respectively. Vaccination coverage was higher in children. The main reason for non-vaccination was absence. No severe adverse events were notified.

CONCLUSIONS/SIGNIFICANCE

The well-accepted mass vaccination campaign reached high coverage in a remote area with a mobile population. Although OCV should not be foreseen as the long-term solution for global cholera control, they should be integrated as an additional tool into the response.

Modeling the effect of water, sanitation, and hygiene and oral cholera vaccine implementation in Haiti

In 2010, toxigenic Vibrio cholerae was newly introduced to Haiti. Because resources are limited, decision-makers need to understand the effect of different preventive interventions. We built a static model to estimate the potential number of cholera cases averted through improvements in coverage in water, sanitation and hygiene (WASH) (i.e., latrines, point-of-use chlorination, and piped water), oral cholera vaccine (OCV), or a combination of both. We allowed indirect effects and non-linear relationships between effect and population coverage. Because there are limited incidence data for endemic cholera in Haiti, we estimated the incidence of cholera over 20 years in Haiti by using data from Malawi. Over the next two decades, scalable WASH interventions could avert 57,949-78,567 cholera cases, OCV could avert 38,569-77,636 cases, and interventions that combined WASH and OCV could avert 71,586-88,974 cases. Rate of implementation is the most influential variable, and combined approaches maximized the effect.

Genomic correlates of variability in immune response to an oral cholera vaccine

Cholera is endemic to many countries. Recent major outbreaks of cholera have prompted World Health Organization to recommend oral cholera vaccination as a public-health strategy. Variation in percentage of seroconversion upon cholera vaccination has been recorded across populations. Vaccine-induced responses are influenced by host genetic differences. We have investigated association between single-nucleotide polymorphic (SNP) loci in and around 296 immunologically relevant genes and total anti-lipopolysaccharide (LPS) antibody response to a killed whole-cell vaccine, comprising LPS from multiple strains of Vibrio cholerae. Titers derived from standard vibriocidal assays were also analyzed to gain further insights on validated SNP associations. Vaccination was administered to 1000 individuals drawn from India. Data on two independent random subsets, each comprising ∼500 vaccinees, were used for discovery of genomic associations and validation, respectively. Significant associations of four SNPs and haplotypes in three genes (MARCO, TNFAIP3 and CXCL12) with AR were discovered and validated, of which two in TNFAIP3 and CXCL12 were also significantly associated with immunity (fourfold increase in vibriocidal titers). CXCL12 is a neutrophil and lymphocyte chemoattractant that is upregulated in response to V. cholerae infection. LPS in the vaccine possibly provides signals that mimic those of the live bacterium. TNFAIP3 promotes intestinal epithelial barrier integrity and provides tight junction protein regulation; possible requirements for adequate response to the vaccine. LPS is a potent activator of innate immune responses and a ligand of MARCO. Variants in this gene have been found to be associated with LPS response, but not with high vibriocidal titer level.

Risk map of cholera infection for vaccine deployment: the eastern Kolkata case

BACKGROUND

Despite advancement of our knowledge, cholera remains a public health concern. During March-April 2010, a large cholera outbreak afflicted the eastern part of Kolkata, India. The quantification of importance of socio-environmental factors in the risk of cholera, and the calculation of the risk is fundamental for deploying vaccination strategies. Here we investigate socio-environmental characteristics between high and low risk areas as well as the potential impact of vaccination on the spatial occurrence of the disease.

METHODS AND FINDINGS

The study area comprised three wards of Kolkata Municipal Corporation. A mass cholera vaccination campaign was conducted in mid-2006 as the part of a clinical trial. Cholera cases and data of the trial to identify high risk areas for cholera were analyzed. We used a generalized additive model (GAM) to detect risk areas, and to evaluate the importance of socio-environmental characteristics between high and low risk areas. During the one-year pre-vaccination and two-year post-vaccination periods, 95 and 183 cholera cases were detected in 111,882 and 121,827 study participants, respectively. The GAM model predicts that high risk areas in the west part of the study area where the outbreak largely occurred. High risk areas in both periods were characterized by poor people, use of unsafe water, and proximity to canals used as the main drainage for rain and waste water. Cholera vaccine uptake was significantly lower in the high risk areas compared to low risk areas.

CONCLUSION

The study shows that even a parsimonious model like GAM predicts high risk areas where cholera outbreaks largely occurred. This is useful for indicating where interventions would be effective in controlling the disease risk. Data showed that vaccination decreased the risk of infection. Overall, the GAM-based risk map is useful for policymakers, especially those from countries where cholera remains to be endemic with periodic outbreaks.

Rapid and scalable plant-based production of a cholera toxin B subunit variant to aid in mass vaccination against cholera outbreaks

INTRODUCTION

Cholera toxin B subunit (CTB) is a component of an internationally licensed oral cholera vaccine. The protein induces neutralizing antibodies against the holotoxin, the virulence factor responsible for severe diarrhea. A field clinical trial has suggested that the addition of CTB to killed whole-cell bacteria provides superior short-term protection to whole-cell-only vaccines; however, challenges in CTB biomanufacturing (i.e., cost and scale) hamper its implementation to mass vaccination in developing countries. To provide a potential solution to this issue, we developed a rapid, robust, and scalable CTB production system in plants.

METHODOLOGY/PRINCIPAL FINDINGS

In a preliminary study of expressing original CTB in transgenic Nicotiana benthamiana, the protein was N-glycosylated with plant-specific glycans. Thus, an aglycosylated CTB variant (pCTB) was created and overexpressed via a plant virus vector. Upon additional transgene engineering for retention in the endoplasmic reticulum and optimization of a secretory signal, the yield of pCTB was dramatically improved, reaching >1 g per kg of fresh leaf material. The protein was efficiently purified by simple two-step chromatography. The GM1-ganglioside binding capacity and conformational stability of pCTB were virtually identical to the bacteria-derived original B subunit, as demonstrated in competitive enzyme-linked immunosorbent assay, surface plasmon resonance, and fluorescence-based thermal shift assay. Mammalian cell surface-binding was corroborated by immunofluorescence and flow cytometry. pCTB exhibited strong oral immunogenicity in mice, inducing significant levels of CTB-specific intestinal antibodies that persisted over 6 months. Moreover, these antibodies effectively neutralized the cholera holotoxin in vitro.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results demonstrated that pCTB has robust producibility in Nicotiana plants and retains most, if not all, of major biological activities of the original protein. This rapid and easily scalable system may enable the implementation of pCTB to mass vaccination against outbreaks, thereby providing better protection of high-risk populations in developing countries.

Effectiveness of the WC/rBS oral cholera vaccine in the prevention of traveler's diarrhea: a prospective cohort study

OBJECTIVE

Traveler's diarrhea (TD) is the most frequent disease among people from industrialized countries who travel to less developed ones, especially sub-Saharan Africa, Southern Asia and South America. The most common bacteria causing TD is enterotoxigenic Escherichia coli (ETEC). The WC/rBS cholera vaccine (Dukoral) has been shown to induce cross-protection against ETEC by means of the B subunit of the cholera toxin. The aim of the study was to evaluate the effectiveness of the WC/rBS cholera vaccine in preventing TD.

METHODS

Between May 1 and September 30 (2007), people seeking pre-travel advice in ten Spanish international vaccination centers were included in a prospective cohort study of travelers to cholera risk countries. The incidence rates of TD were adjusted for variables whose frequencies were statistically different (entry point 0.10) between the vaccinated and non-vaccinated cohorts.

FINDINGS

The vaccinated cohort (n = 544 travelers) included people vaccinated with the WC/rBS cholera vaccine, and the non-vaccinated cohort (n = 530 travelers) by people not vaccinated. The cumulative incidence rate of TD was 1.69 in vaccinated and 2.14 in non-vaccinated subjects. The adjusted relative risk of TD in vaccinated travelers was 0.72 (95% CI: 0.58-0.88) and the adjusted vaccination effectiveness was 28% (95% CI: 12-42).

CONCLUSIONS

The WC/rBS cholera vaccine prevents TD in 2 out of 7 travelers (preventive fraction: 28%). The number needed to vaccinate (NNV) to prevent 1 case of TD is 10.

Costs of illness due to cholera, costs of immunization and cost-effectiveness of an oral cholera mass vaccination campaign in Zanzibar

BACKGROUND

The World Health Organization (WHO) recommends oral cholera vaccines (OCVs) as a supplementary tool to conventional prevention of cholera. Dukoral, a killed whole-cell two-dose OCV, was used in a mass vaccination campaign in 2009 in Zanzibar. Public and private costs of illness (COI) due to endemic cholera and costs of the mass vaccination campaign were estimated to assess the cost-effectiveness of OCV for this particular campaign from both the health care provider and the societal perspective.

METHODOLOGY/PRINCIPAL FINDINGS

Public and private COI were obtained from interviews with local experts, with patients from three outbreaks and from reports and record review. Cost data for the vaccination campaign were collected based on actual expenditure and planned budget data. A static cohort of 50,000 individuals was examined, including herd protection. Primary outcome measures were incremental cost-effectiveness ratios (ICER) per death, per case and per disability-adjusted life-year (DALY) averted. One-way sensitivity and threshold analyses were conducted. The ICER was evaluated with regard to WHO criteria for cost-effectiveness. Base-case ICERs were USD 750,000 per death averted, USD 6,000 per case averted and USD 30,000 per DALY averted, without differences between the health care provider and the societal perspective. Threshold analyses using Shanchol and assuming high incidence and case-fatality rate indicated that the purchase price per course would have to be as low as USD 1.2 to render the mass vaccination campaign cost-effective from a health care provider perspective (societal perspective: USD 1.3).

CONCLUSIONS/SIGNIFICANCE

Based on empirical and site-specific cost and effectiveness data from Zanzibar, the 2009 mass vaccination campaign was cost-ineffective mainly due to the relatively high OCV purchase price and a relatively low incidence. However, mass vaccination campaigns in Zanzibar to control endemic cholera may meet criteria for cost-effectiveness under certain circumstances, especially in high-incidence areas and at OCV prices below USD 1.3.

Safety of the recombinant cholera toxin B subunit, killed whole-cell (rBS-WC) oral cholera vaccine in pregnancy

Introduction

Mass vaccinations are a main strategy in the deployment of oral cholera vaccines. Campaigns avoid giving vaccine to pregnant women because of the absence of safety data of the killed whole-cell oral cholera (rBS-WC) vaccine. Balancing this concern is the known higher risk of cholera and of complications of pregnancy should cholera occur in these women, as well as the lack of expected adverse events from a killed oral bacterial vaccine.

Methodology/Principal Findings

From January to February 2009, a mass rBS-WC vaccination campaign of persons over two years of age was conducted in an urban and a rural area (population 51,151) in Zanzibar. Pregnant women were advised not to participate in the campaign. More than nine months after the last dose of the vaccine was administered, we visited all women between 15 and 50 years of age living in the study area. The outcome of pregnancies that were inadvertently exposed to at least one oral cholera vaccine dose and those that were not exposed was evaluated. 13,736 (94%) of the target women in the study site were interviewed. 1,151 (79%) of the 1,453 deliveries in 2009 occurred during the period when foetal exposure to the vaccine could have occurred. 955 (83%) out of these 1,151 mothers had not been vaccinated; the remaining 196 (17%) mothers had received at least one dose of the oral cholera vaccine. There were no statistically significant differences in the odds ratios for birth outcomes among the exposed and unexposed pregnancies.

Conclusions/Significance

We found no statistically significant evidence of a harmful effect of gestational exposure to the rBS-WC vaccine. These findings, along with the absence of a rational basis for expecting a risk from this killed oral bacterial vaccine, are reassuring but the study had insufficient power to detect infrequent events.

Trial Registration

ClinicalTrials.gov NCT00709410

Pregnant women are more vulnerable to complications of cholera than other people. It would be helpful to include pregnant women in vaccination campaigns against cholera but pregnant women and their unborn children are highly vulnerable to the potential adverse effects of biological products such as vaccines. The safety of oral cholera vaccines in pregnant women has up to now not been evaluated. During a large mass cholera vaccination campaign in Zanzibar in 2009, women were advised not to participate if they thought they may be pregnant. The large majority (955 or 83%) of women residing in the study area who were to be pregnant during the 9 months following the vaccinations did not participate in the campaign. The remaining 196 (17%) women received the vaccine. A comparison between vaccine exposed and unexposed pregnancies did not reveal any significant differences in outcome between the two groups. The small number of miscarriages, infant deaths and ill infants was similarly distributed between the two groups. These findings are reassuring but continued monitoring of this vaccine when given during pregnancy is recommended.

Evaluation and use of surveillance system data toward the identification of high-risk areas for potential cholera vaccination: a case study from Niger

BACKGROUND

In 2008, Africa accounted for 94% of the cholera cases reported worldwide. Although the World Health Organization currently recommends the oral cholera vaccine in endemic areas for high-risk populations, its use in Sub-Saharan Africa has been limited. Here, we provide the principal results of an evaluation of the cholera surveillance system in the region of Maradi in Niger and an analysis of its data towards identifying high-risk areas for cholera.

RESULTS

We evaluated the cholera surveillance data using a standard CDC protocol, through interviews with heads of the system, and a review of cholera data collected between 2006-2009. The surveillance system was found to be sufficiently reliable to be able to utilize the data for the detection of high risk areas for cholera vaccination. Temporal, geographic and socio-demographic analyses of cholera cases indicated that between 2006 and 2009, 433 cholera cases were reported in the Maradi region of Niger. Two deprived neighborhoods of the region's capital city, Bagalam and Yandaka, represented 1% of the regional population and 21% of the cholera cases, reaching a yearly incidence rate of 3 per 1000 in 2006 and 2008, respectively.

CONCLUSIONS

The results of this evaluation suggest that the reporting sensitivity of the surveillance system is sufficient, to appropriately classify the region as cholera endemic. Additionally, two overcrowded neighborhoods in the regional capital met WHO criteria for consideration for cholera vaccination.

Simple, direct conjugation of bacterial O-SP-core antigens to proteins: development of cholera conjugate vaccines

Bacterial O-SP-core antigens can be conjugated to proteins in the same, simple way as synthetic, linker-equipped carbohydrates by applying squaric acid chemistry. Introduction of spacers (linkers) to either O-SP-core antigens or protein carriers, which is involved in commonly applied protocols, is not required. The newly developed method described here consists of preparation of a squaric acid monoester derivative of O-SP-core antigen, utilizing the amino group inherent in the core, and reaction of the monoester with the carrier protein. The intermediate monoester can be easily purified; its conjugation can be monitored by SELDI-TOF mass spectrometry and, thus, readily controlled, since the conjugation can be terminated when the desired carbohydrate-protein ratio is reached. Here, we describe production of conjugates containing the O-SP-core antigen of Vibrio cholerae O1, the major cause of cholera, a severe dehydrating diarrheal disease of humans. The resultant products are recognized by convalescent phase sera from patients recovering from cholera in Bangladesh, and anti-O-SP-core-protein responses correlate with plasma antilipopolysaccharide and vibriocidal responses, which are the primary markers of protection from cholera. The results suggest that such conjugates have potential as vaccines for cholera and other bacterial diseases.

Efficacy of a low-cost, inactivated whole-cell oral cholera vaccine: results from 3 years of follow-up of a randomized, controlled trial

BACKGROUND

Killed oral cholera vaccines (OCVs) have been licensed for use in developing countries, but protection conferred by licensed OCVs beyond two years of follow-up has not been demonstrated in randomized, clinical trials.

METHODS/PRINCIPAL FINDINGS

We conducted a cluster-randomized, placebo-controlled trial of a two-dose regimen of a low-cost killed whole cell OCV in residents 1 year of age and older living in 3,933 clusters in Kolkata, India. The primary endpoint was culture-proven Vibrio cholerae O1 diarrhea episodes severe enough to require treatment in a health care facility. Of the 66,900 fully dosed individuals (31,932 vaccinees and 34,968 placebo recipients), 38 vaccinees and 128 placebo-recipients developed cholera during three years of follow-up (protective efficacy 66%; one-sided 95%CI lower bound = 53%, p<0.001). Vaccine protection during the third year of follow-up was 65% (one-sided 95%CI lower bound = 44%, p<0.001). Significant protection was evident in the second year of follow-up in children vaccinated at ages 1-4 years and in the third year in older age groups.

CONCLUSIONS/SIGNIFICANCE

The killed whole-cell OCV conferred significant protection that was evident in the second year of follow-up in young children and was sustained for at least three years in older age groups. Continued follow-up will be important to establish the vaccine's duration of protection.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00289224.

Natural cholera infection-derived immunity in an endemic setting

BACKGROUND

Live oral cholera vaccines may protect against cholera in a manner similar to natural cholera infections. However, information on which to base these vaccines is limited.

METHODS

The study was conducted in a cholera-endemic population in Bangladesh. Patients with cholera (index patients) detected between 1991 and 2000 were age-matched to 4 cholera-free controls and then followed up during the subsequent 3 years.

RESULTS

El Tor cholera was associated with a 65% (95% confidence interval [CI], 37%-81%; P < .001) lower risk of a subsequent El Tor episode. Reduction of the risk of subsequent El Tor cholera was similar for children < 5 years and for older persons and was sustained during all 3 years of follow-up. Having El Tor Inaba cholera was associated with lower risks of both El Tor Inaba and El Tor Ogawa cholera, but having El Tor Ogawa cholera was associated only with a reduced risk of El Tor Ogawa cholera. O139 cholera was associated with a 63% (95% CI, -61% to 92%; P = .18) lower risk of subsequent O139 cholera, but there was no evidence of cross-protection between the O1 and O139 serogroups.

CONCLUSIONS

Live oral cholera vaccines designed to protect against the O1 and O139 serogroups should contain at least the Inaba serotype and strains of both serogroups.

Safety and immunogenicity study of a killed bivalent (O1 and O139) whole-cell oral cholera vaccine Shanchol, in Bangladeshi adults and children as young as 1 year of age

BACKGROUND

Safety and immunogenicity study of an oral, killed, bivalent whole-cell, cholera vaccine, Shanchol was carried out in Bangladeshi participants. This study was conducted prior to initiating a feasibility study in Bangladesh.

STUDY PARTICIPANTS

The double-blind, randomized placebo controlled study was carried out in adults (18-45 years), toddlers (2-5 years) and younger children (12-23 months). Two doses of the vaccine/placebo were given 14 days apart.

RESULTS

Shanchol did not elicit major adverse events in any age group. Vibriocidal antibody responses in adults were 60% against Vibrio cholerae O1 Inaba, 72% against V. cholerae O1 Ogawa and 21% against V. cholerae O139. In toddlers, responses were 84%, 75% and 64% and in younger children it was 74%, 78% and 54% against Inaba, Ogawa and O139 serotypes. The responses in all ages were higher in vaccinees compared to pre-immune titers or to responses in placebo recipients (P<0.001). Plasma IgA antibody response to O1 Inaba LPS was seen in 61%, 73% and 45% of adults, toddlers and younger children, respectively.

CONCLUSIONS

The safety and immunogenicity data for Shanchol is promising and warrants future use in large scale trial in cholera endemic areas, high risk Bangladeshi population and in other countries in the region.

Antigen-specific memory B-cell responses in Bangladeshi adults after one- or two-dose oral killed cholera vaccination and comparison with responses in patients with naturally acquired cholera

The mediators of protective immunity against cholera are currently unknown, but memory B-cell responses may play a central role in facilitating long-term and anamnestic responses against Vibrio cholerae, the cause of cholera. We compared memory B-cell responses in adults with natural cholera in Bangladesh (n = 70) to responses in Bangladeshi adults after one-dose (n = 30) or two-dose (n = 30) administration of an oral killed cholera vaccine, WC-rBS (Dukoral; Crucell), assessing the responses at the acute stage of disease or prevaccination and then on days 3, 30, 90, 180, 270, and 360. Individuals with natural cholera developed prominent vibriocidal and plasma anti-cholera toxin B subunit (CtxB) and lipopolysaccharide (LPS) IgG and IgA responses, but these responses returned to baseline by 1 year of follow-up. Vaccinees developed plasma anti-CtxB and anti-LPS IgG and IgA responses that were generally comparable to those in individuals recovering from natural disease, but vibriocidal responses were lower in vaccinees than in infected patients. Individuals recovering from natural disease developed memory B-cell IgG and IgA anti-CtxB and anti-LPS responses by day 30, and these responses were detectable through at least days 180 to 360. In contrast, we detected no IgA or IgG memory B-cell responses to LPS in vaccinees; anti-CtxB IgA responses were only detectable on day 30, and anti-CtxB IgG responses were detectable until days 90 to 180, compared to days 270 to 360 in patients. These findings may explain in part the relatively short-term protection afforded by oral cholera vaccination compared to natural disease.

The case for reactive mass oral cholera vaccinations

Introduction

The outbreak of cholera in Zimbabwe intensified interest in the control and prevention of cholera. While there is agreement that safe water, sanitation, and personal hygiene are ideal for the long term control of cholera, there is controversy about the role of newer approaches such as oral cholera vaccines (OCVs). In October 2009 the Strategic Advisory Group of Experts advised the World Health Organization to consider reactive vaccination campaigns in response to large cholera outbreaks. To evaluate the potential benefit of this pivotal change in WHO policy, we used existing data from cholera outbreaks to simulate the number of cholera cases preventable by reactive mass vaccination.

Methods

Datasets of cholera outbreaks from three sites with varying cholera endemicity—Zimbabwe, Kolkata (India), and Zanzibar (Tanzania)—were analysed to estimate the number of cholera cases preventable under differing response times, vaccine coverage, and vaccine doses.

Findings

The large cholera outbreak in Zimbabwe started in mid August 2008 and by July 2009, 98,591 cholera cases had been reported with 4,288 deaths attributed to cholera. If a rapid response had taken place and half of the population had been vaccinated once the first 400 cases had occurred, as many as 34,900 (40%) cholera cases and 1,695 deaths (40%) could have been prevented. In the sites with endemic cholera, Kolkata and Zanzibar, a significant number of cases could have been prevented but the impact would have been less dramatic. A brisk response is required for outbreaks with the majority of cases occurring during the early weeks. Even a delayed response can save a substantial number of cases and deaths in long, drawn-out outbreaks. If circumstances prevent a rapid response there are good reasons to roll out cholera mass vaccination campaigns well into the outbreak. Once a substantial proportion of a population is vaccinated, outbreaks in subsequent years may be reduced if not prevented. A single dose vaccine would be of advantage in short, small outbreaks.

Conclusions

We show that reactive vaccine use can prevent cholera cases and is a rational response to cholera outbreaks in endemic and non-endemic settings. In large and long outbreaks a reactive vaccination with a two-dose vaccine can prevent a substantial proportion of cases. To make mass vaccination campaigns successful, it would be essential to agree when to implement reactive vaccination campaigns and to have a dynamic and determined response team that is familiar with the logistic challenges on standby. Most importantly, the decision makers in donor and recipient countries have to be convinced of the benefit of reactive cholera vaccinations.

Cholera outbreaks have had catastrophic impact on societies for centuries. Despite more than half a century of advocacy for safe water, sanitation and hygiene, approximately 100,000 cholera cases and 5,000 deaths were reported in Zimbabwe between August 2008 and by July 2009. Safe and effective oral cholera vaccines have been licensed and used by affluent tourists for more than a decade to prevent cholera. We asked whether oral cholera vaccines could be used to protect high risk populations at a time of cholera. We calculated how many cholera cases could have been prevented if mass cholera vaccinations would have been implemented in reaction to past cholera outbreaks. We estimate that determined, well organized mass vaccination campaigns could have prevented 34,900 (40%) cholera cases and 1,695 deaths (40%) in Zimbabwe. In the sites with endemic cholera, Kolkata and Zanzibar, a significant number of cases could have been prevented but the impact would have been less dramatic. The barriers which currently prevent the implementation of mass vaccinations, including but not only the cost to purchase the vaccine, seem insurmountable. A concerted effort of donors and key decision makers will be needed to offer better protection to populations at risk.

[Challenge clinical trial for evaluation of a vaccine candidate strain against cholera]

INTRODUCTION

live attenuated oral Vibrio cholerae Ol El Tor, Ogawa strain 638 has demonstrated to be well tolerated and immunogenic when administrated orally in studies carried out in healthy volunteers.

OBJECTIVES

to evaluate the protection against cholera infection in a challenge clinical trial, for the technological and pharmaceutical scale-up of this vaccinal candidate as active ingredient at industrial level.

METHODS

a total of 21 healthy volunteers were involved in this trial; the vaccine candidate was administered to 12 of them and the remaining nine were given the placebo. Twenty eight days later, all of them received an infective dose of a V. cholerae virulent strain.

RESULTS

diarrheas were observed in 7 out of 9 placebos whereas not a single vaccinated volunteer showed diarrheas. More frequent and intense loose stools were found in the placebo volunteers with O-blood group. All volunteers in he placebo group excreted V. cholerae, but only three (25%) out of the 12 vaccinated volunteers did so.

CONCLUSION

in this challenge clinical trial model, the 638 strain proved to protect people against the diarrhea caused by a virulent V. cholerae strain.

Vaccines for preventing cholera: killed whole cell or other subunit vaccines (injected)

BACKGROUND

Injected cholera vaccines are rarely used today, although they may have some benefit. It is valuable to summarize the evidence for effectiveness of injected cholera vaccines for comparison with newer oral vaccines (subject of a separate Cochrane Review).

OBJECTIVES

To evaluate killed whole cell (KWC) cholera vaccines and other inactive subunit vaccines (administered by injection) for preventing cholera and death, and to evaluate the adverse effects.

SEARCH STRATEGY

In September 2008, we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (The Cochrane Library 2008, Issue 3), EMBASE, and LILACS. We also searched reference lists and handsearched the journal Vaccine up to 1997.

SELECTION CRITERIA

Randomized and quasi-randomized controlled trials comparing injected cholera vaccines (KWC or other inactive subunit) with placebo, control vaccines, or no intervention in adults and children irrespective of immune status or special risk category.

DATA COLLECTION AND ANALYSIS

Two authors extracted data and assessed trial methodological quality independently. Dichotomous data were reported using the risk ratio (RR) with 95% confidence intervals (CI). Vaccine efficacies were also calculated (% vaccine efficacy = (1-RR) x 100%).

MAIN RESULTS

Sixteen trials, involving over one million adults, children and infants, fulfilled the inclusion criteria. Twenty-four comparisons reported on vaccine efficacy (cholera cases and/or deaths) and 11 comparisons considered adverse effects (nine reported on both). Compared to placebo, vaccinees had a reduced risk of death from cholera (RR 0.49, 95% CI 0.25 to 0.93; 837,442 participants) and a reduced risk of contracting cholera at 12 months (RR 0.52, 95% CI 0.42 to 0.65, random-effects model; 1,512,573 participants). This translates to an efficacy of 48%, 95% confidence interval 35% to 58%. Significant protection lasted for two years, even after only a single dose, and for three years with an annual booster. Children over five years and adults were protected for up to three years, while children under five years were protected for up to a year. Injected cholera vaccines were associated with more systemic and local adverse effects compared to placebo, but these were not severe or life-threatening.

AUTHORS' CONCLUSIONS

Injected cholera vaccines appear to be safe and relatively more effective than usually realized. Protection against cholera persists for up to two years following a single dose of vaccine, and for three years with an annual booster. However, they have been superseded by oral vaccines.

Rabies glycoprotein fused with B subunit of cholera toxin expressed in tobacco plants folds into biologically active pentameric protein

The pentameric B subunit of cholera toxin (CtxB) is an efficient mucosal adjuvant for vaccines. We report the expression of a chimeric protein comprising the synthetic cholera toxin B subunit fused at its C-terminal with rabies surface glycoprotein (G protein) in tobacco plants. The approximately 80.3 kDa fusion polypeptide expressed at 0.4% of the total soluble protein in leaves of the selected transgenic lines. The fusion protein formed a approximately 403 kDa pentameric protein which was functionally active in binding to GM1 receptor. The plant-made protein had a higher affinity for GM1 receptor than the native bacterial CtxB. The pentameric fusion protein was recognized by the anti-cholera toxin as well as anti-rabies antibodies. Its immuno-protective ability against rabies remains to be examined.

Chloroplast-derived vaccine antigens confer dual immunity against cholera and malaria by oral or injectable delivery

Cholera and malaria are major diseases causing high mortality. The only licensed cholera vaccine is expensive; immunity is lost in children within 3 years and adults are not fully protected. No vaccine is yet available for malaria. Therefore, in this study, the cholera toxin-B subunit (CTB) of Vibrio cholerae fused to malarial vaccine antigens apical membrane antigen-1 (AMA1) and merozoite surface protein-1 (MSP1) was expressed in lettuce and tobacco chloroplasts. Southern blot analysis confirmed homoplasmy and stable integration of transgenes. CTB-AMA1 and CTB-MSP1 fusion proteins accumulated up to 13.17% and 10.11% (total soluble protein, TSP) in tobacco and up to 7.3% and 6.1% (TSP) in lettuce, respectively. Nine groups of mice (n = 10/group) were immunized subcutaneously (SQV) or orally (ORV) with purified antigens or transplastomic tobacco leaves. Significant levels of antigen-specific antibody titres of immunized mice completely inhibited proliferation of the malarial parasite and cross-reacted with the native parasite proteins in immunoblots and immunofluorescence studies. Protection against cholera toxin challenge in both ORV (100%) and SQV (89%) mice correlated with CTB-specific titres of intestinal, serum IgA and IgG1 in ORV and only IgG1 in SQV mice, but no other immunoglobulin. Increasing numbers of interleukin-10(+) T cell but not Foxp3(+) regulatory T cells, suppression of interferon-gamma and absence of interleukin-17 were observed in protected mice, suggesting that immunity is conferred via the Tr1/Th2 immune response. Dual immunity against two major infectious diseases provided by chloroplast-derived vaccine antigens for long-term (>300 days, 50% of mouse life span) offers a realistic platform for low cost vaccines and insight into mucosal and systemic immunity.

[Analysis of safety and effects on the oral whole cell/recombinant B subunit cholera vaccine in university students and workers]

OBJECTIVE

To evaluate the safety, immunogenicity and protective efficiency of the oral whole cell/recombinant B subunit cholera vaccine in Beijing Olympic volunteers and workers.

METHOD

Analyzing the incidence rate of adverse reaction and Protective Rate (PR) after taking the vaccine in Olympic volunteers in 6 universities in Beijing; comparing the anti-cholera toxin (CT) detected with ELISA prior and after taking the vaccine in Olympic workers.

RESULTS

The total rate of adverse reaction of Olympic volunteers was 0.38%; the main side effects were gastrointestinal symptoms, such as bellyache and diarrhea which were mild and temple; the acute diarrhea incidence rate of Olympic volunteers after taking the vaccine was significantly lower than those not taking it, the PR was 76.27%; the positive rate of anti-CT of Olympic workers after taking the vaccine was significantly higher than those before taking it, the levels of anti-CT titers declined after 6 months since they had taken the vaccine.

CONCLUSION

The results from above two observed population indicate that the oral rBS-WC cholera vaccine is efficient and safe.

Efficacy and safety of a modified killed-whole-cell oral cholera vaccine in India: an interim analysis of a cluster-randomised, double-blind, placebo-controlled trial

BACKGROUND

Oral cholera vaccines consisting of killed whole cells have been available for many years, but they have not been used extensively in populations with endemic disease. An inexpensive, locally produced oral killed-whole-cell vaccine has been used in high-risk areas in Vietnam. To expand the use of this vaccine, it was modified to comply with WHO standards. We assessed the efficacy and safety of this modified vaccine in a population with endemic cholera.

METHODS

In this double-blind trial, 107 774 non-pregnant residents of Kolkata, India, aged 1 year or older, were cluster-randomised by dwelling to receive two doses of either modified killed-whole-cell cholera vaccine (n=52 212; 1966 clusters) or heat-killed Escherichia coli K12 placebo (n=55 562; 1967 clusters), both delivered orally. Randomisation was done by computer-generated sequence in blocks of four. The primary endpoint was prevention of episodes of culture-confirmed Vibrio cholerae O1 diarrhoea severe enough for the patient to seek treatment in a health-care facility. We undertook an interim, per-protocol analysis at 2 years of follow-up that included individuals who received two completely ingested doses of vaccine or placebo. We assessed first episodes of cholera that occurred between 14 days and 730 days after receipt of the second dose. This study is registered with ClinicalTrials.gov, number NCT00289224.

FINDINGS

31 932 participants assigned to vaccine (1721 clusters) and 34 968 assigned to placebo (1757 clusters) received two doses of study treatment. There were 20 episodes of cholera in the vaccine group and 68 episodes in the placebo group (protective efficacy 67%; one-tailed 99% CI, lower bound 35%, p<0.0001). The vaccine protected individuals in age-groups 1.0-4.9 years, 5.0-14.9 years, and 15 years and older, and protective efficacy did not differ significantly between age-groups (p=0.28). We recorded no vaccine-related serious adverse events.

INTERPRETATION

This modified killed-whole-cell oral vaccine, compliant with WHO standards, is safe, provides protection against clinically significant cholera in an endemic setting, and can be used in children aged 1.0-4.9 years, who are at highest risk of developing cholera in endemic settings.

FUNDING

Bill & Melinda Gates Foundation, Swedish International Development Cooperation Agency, Governments of South Korea, Sweden, and Kuwait.

A comparison of clinical and immunologic features in children and older patients hospitalized with severe cholera in Bangladesh

BACKGROUND

: Infection with Vibrio cholerae induces protection from subsequent severe disease, suggesting that an effective vaccine could be an important preventive strategy. Available vaccines provide less protection against cholera than natural infection, particularly in children.

METHODS

: We examined a cohort of 121 children (2 years-12 years of age) and 276 older patients (>12 years of age) hospitalized with cholera in Dhaka, Bangladesh over a 4-year period, to compare clinical features in older patients and children and immune responses to key antigens.

RESULTS

: Older patients had more severe disease. Children with cholera were more commonly retinol deficient, while zinc deficiency was equally prevalent in both groups. Children developed higher vibriocidal and serum immune responses to the B subunit of cholera toxin (CTB). In contrast, older patients mounted higher immune responses to 2 other key V. cholerae antigens, the lipopolysaccharide (LPS) and toxin coregulated pilus antigens (TcpA). We compared immune responses following infection with those occurring after receipt of a live, oral vaccine in both children and older patients in Bangladesh, during a similar time period. The response rates for vibriocidal and LPS antibodies were higher after infection than after vaccination. Both vaccinated older patients and children responded poorly to CTB and TcpA.

CONCLUSIONS

: Although children developed vigorous vibriocidal and CTB-specific responses following infection, they had lessened responses to LPS and TcpA compared with older patients, as well as lessened responses to vaccination. More studies need to be carried out to determine factors, including micronutrient interventions that can improve responses in children to both natural infection and vaccination.

InactiveVibrio choleraewhole-cell vaccine-loaded biodegradable microparticles:in vitrorelease and oral vaccination

An approach is proposed using Vibrio cholerae (VC)-loaded microparticles as oral vaccine delivery systems for improved vaccine bioavailability and increased therapeutic efficacy. The VC-loaded microparticles were prepared with 50:50 poly(DL-lactide-co-glycolide) (PLG), 75:25 poly(DL-lactide-co-glycolide) and poly(lactide acid) (PLA)/PEG blend copolymers by the solvent evaporation method. VC was successfully entrapped in three types of microparticles with loading efficiencies and loading levels as follows: 50:50 PLG systems: 97.8% and 55.4 +/- 6.9 micro g/mg; 75:25 PLG systems: 89.2% and 46.5 +/- 4.4 micro g/mg; PLA/PEG-blended systems: 82.6% and 53.7 +/- 5.8 micro g/mg. The different distributions of VC in the core region and on the surface were as follows: 50:50 PLG systems 25.7 +/- 1.9 and 6.2 +/- 0.9 micro g/mg; 75:25 PLG systems: 25.8 +/- 2.2 and 3.6 +/- 0.4 micro g/mg; PLA/PEG-blended systems: 32.4 +/- 2.1 and 5.2 +/- 1.0 micro g/mg, respectively. In vitro active release of VC was affected mainly by matrix type and VC-loaded location in microparticles. The therapeutic immunogenic potential of VC loaded with 50:50 PLG, 75:25 PLG and PLA/PEG-blended microparticles was evaluated in adult mice by oral immunization. Significantly higher antibody responses and serum immunoglobin Ig G, IgA and IgM responses were obtained when sera from both VC-loaded 75:25 PLG and PLA/PEG-blended microparticles immunized mice were titrated against VC. The most immunogenicity in evoking serum IgG, IgA and IgM responses was immunized by VC-loaded PLA/PEG-blended microparticles, and with VC challenge in mice, the survival rate (91.7%).

A randomized, placebo-controlled trial of the bivalent killed, whole-cell, oral cholera vaccine in adults and children in a cholera endemic area in Kolkata, India

OBJECTIVES

An effective vaccine against cholera has been used for public health purposes in Vietnam since the 1990s. This vaccine was reformulated to meet WHO requirements. We assessed the safety and immunogenicity of the reformulated bivalent (Vibrio cholerae 01 and 0139) killed whole cell oral vaccine in a cholera endemic area in Kolkata, India.

DESIGN

Double-blind, randomized, placebo controlled trial.

SETTING

The trial was conducted in the clinical trial ward of the Infectious Diseases Hospital in Kolkata, India.

PARTICIPANTS

The participants were 101 healthy adults (males and non-pregnant females) aged 18-40 years and 100 healthy children (males and non-pregnant females) aged 1-17 years.

INTERVENTIONS

Participants were randomized to receive either the bivalent killed whole cell oral cholera vaccine or placebo (killed oral Escherichia coli K12).

OUTCOME MEASURES

For safety: proportion of subjects with adverse events during the duration of study participation. For immunogenicity: Proportion of subjects who had a > or = 4-fold rise in serum vibriocidal antibody titers 14 days after the second dose of vaccine or placebo.

RESULTS

Adverse reactions were observed with similar frequency among vaccine and placebo recipients in both age groups. Among adults 4% of vaccine and 8% of placebo recipients and among children 4% of vaccine and 2% of placebo recipients had at least one adverse event within 28 days of the first dose of the vaccine. Following immunization, 53% of adult and 80% of children vaccinees showed a > or = 4 fold rise in serum V. cholerae O1 vibriocidal antibody titers. A less pronounced response to V. cholerae O139 vibriocidal antibody titers post-immunization was noted among vaccinees.

CONCLUSIONS

We found the vaccine to be safe and immunogenic in a cholera-endemic area in India.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00119197.

Expression of toxin co-regulated pilus subunit A (TCPA) of Vibrio cholerae and its immunogenic epitopes fused to cholera toxin B subunit in transgenic tomato (Solanum lycopersicum)

For protection against cholera, it is important to develop efficient vaccine capable of inducing anti-toxin as well as anti-colonizing immunity against Vibrio cholerae infections. Earlier, expression of cholera toxin B subunit (CTB) in tomato was reported by us. In the present investigation, toxin co-regulated pilus subunit A (TCPA), earlier reported to be an antigen capable of providing anti-colonization immunity, has been expressed in tomato. Further, to generate more potent combinatorial antigens, nucleotides encoding P4 or P6 epitope of TCPA were fused to cholera toxin B subunit gene (ctxB) and expressed in tomato. Presence of transgenes in the tomato genome was confirmed by PCR and expression of genes was confirmed at transcript and protein level. TCPA, chimeric CTB-P4 and CTB-P6 proteins were also expressed in E. coli. TCPA protein expressed in E. coli was purified to generate anti-TCPA antibodies in rabbit. Immunoblot and G(M1)-ELISA verified the synthesis and assembly of pentameric chimeric proteins in fruit tissue of transgenic tomato plants. The chimeric protein CTB-P4 and CTB-P6 accumulated up to 0.17 and 0.096% of total soluble protein (TSP), respectively, in tomato fruits. Whereas expression of TCPA, CTB-P4 and CTB-P6 in E. coli can be utilized for development of conventional vaccine, expression of these antigens which can provide both anti-toxin as well as anti-colonization immunity, has been demonstrated in plants, in a form which is potentially capable of inducing immune response against cholera infection.

Vaccines for cholera control: does herd immunity play a role

The author discusses a new study that mathematically simulated different vaccine coverage levels in the Matlab region of Bangladesh using a historic vaccine trial dataset.

Controlling endemic cholera with oral vaccines

BACKGROUND

Although advances in rehydration therapy have made cholera a treatable disease with low case-fatality in settings with appropriate medical care, cholera continues to impose considerable mortality in the world's most impoverished populations. Internationally licensed, killed whole-cell based oral cholera vaccines (OCVs) have been available for over a decade, but have not been used for the control of cholera. Recently, these vaccines were shown to confer significant levels of herd protection, suggesting that the protective potential of these vaccines has been underestimated and that these vaccines may be highly effective in cholera control when deployed in mass immunization programs. We used a large-scale stochastic simulation model to investigate the possibility of controlling endemic cholera with OCVs.

METHODS AND FINDINGS

We construct a large-scale, stochastic cholera transmission model of Matlab, Bangladesh. We find that cholera transmission could be controlled in endemic areas with 50% coverage with OCVs. At this level of coverage, the model predicts that there would be an 89% (95% confidence interval [CI] 72%-98%) reduction in cholera cases among the unvaccinated, and a 93% (95% CI 82%-99%) reduction overall in the entire population. Even a more modest coverage of 30% would result in a 76% (95% CI 44%-95%) reduction in cholera incidence for the population area covered. For populations that have less natural immunity than the population of Matlab, 70% coverage would probably be necessary for cholera control, i.e., an annual incidence rate of < or = 1 case per 1,000 people in the population.

CONCLUSIONS

Endemic cholera could be reduced to an annual incidence rate of < or = 1 case per 1,000 people in endemic areas with biennial vaccination with OCVs if coverage could reach 50%-70% depending on the level of prior immunity in the population. These vaccination efforts could be targeted with careful use of ecological data.

Exploiting cholera vaccines as a versatile antigen delivery platform

The development of safe, immunogenic and protective cholera vaccine candidates makes possible their use as a versatile antigen delivery platform. Foreign antigens can be delivered to the immune system with cholera vaccines by expressing heterologous antigens in live attenuated vectors, as fusion proteins with cholera toxin subunits combined with inactivated Vibrio cholerae whole cells or by exposing them on the surface of V. cholerae ghosts. Progress in our understanding of the genes expressed by V. cholerae during infection creates unprecedented opportunities to develop an improved generation of vaccine vectors to induce immune protection against a broad range of pathogenic organisms.

A semi-automated vibriocidal assay for improved measurement of cholera vaccine-induced immune responses

Vibriocidal antibody assay has been a surrogate standard assay in the evaluation of cholera vaccine efficacy because it has a good correlation with protection. Although the optical density-based vibriocidal assay in a 96-well microtiter-plate format is widely used in clinical trials, it has limitations as vibriocidal titers are altered by incubation time and samples with the same end-point titers could have potentially different vibriocidal kinetics. In the present study, we developed an improved agar-plate assay coupled with an automated colony counting system. Through testing 30 pairs of human sera from vaccinees administered with a cholera vaccine or placebo, these two assays showed good correlations for the vibriocidal titers and fold increases in titers between pre- and post-vaccinated sera as determined by the Pearson correlation coefficient and the Regression coefficient. Notably, the newly-developed semi-automated assay demonstrated that serum samples with the same end-point titers turned out to have distinct vibriocidal kinetics that were not distinguishable by the microtiter-plate assay. The semi-automated assay responded specifically to Vibrio cholerae but not to irrelevant bacteria such as Salmonella typhi and Escherichia coli. These results demonstrate that the semi-automated assay provides better sensitivity, accuracy, and stability of the assay results with minimized efforts than conventional microtiter-plate assay and could provide a useful tool as an in vitro surrogate assay for the evaluation of cholera vaccine efficacy.

[Examples for vaccines against diarrheal diseases--rotavirus and traveller's diarrhea]

Diarrheal diseases constitute one of the most important health problems worldwide. Children less than 5 years, living in developing countries, are particularly in danger with respect to the incidence and severity of the gastrointestinal disorders. Travelers to developing countries are also at risk to develop diarrheal disorders; around 30-50% of them acquire so called "travelers's diarrhea" caused by bacteria, viruses or protozoa. It has been estimated that approximately 30-70% of diarrhea are due to bacteria, of which the most frequently detected enteric pathogens are non-invasive, enterotoxigenic Escherichia coli (ETEC). Their exotoxins, the heat stabile (ST) and the heat labile (LT) toxins are in large part responsible for the pathogenicity of the bacteria. About 20% of cases of traveler's diarrhea are caused by LT producing ETEC. This heat labile toxin exhibits a 80% sequence homology with cholera toxin. The presently available vaccine against cholera (Dukoral) contains inactivated Vibrio cholerae bacteria and the recombinant non-toxic B subunit of cholera toxin. Consequently, this vaccine displays also some efficacy against traveler's diarrhoea with up to 25 % of travelers being protected against this disease. Rotaviruses are the leading recognized cause of diarrhoea-related illness and deaths among infants worldwide in developing and industrialized countries. Based on the high incidence of this disease two oral vaccines have been developed and are available in Europe in 2007. Due to the impact of rotavirus diseases also in Austria vaccination against this disease has been already suggested in the Austrian vaccination schedules for infants from 6-24 weeks of age. One of the two vaccines, Rotarix, is an attenuated monovalent vaccine with a broad cross-reactivity against the most frequent serotypes. The second one, RotaTeq, is a pentavalent attenuated vaccine containing 5 human-bovine reassortants. Both vaccines display 85-98% efficacy against severe rotavirus disease and an excellent tolerability with no difference in side reactions to the placebo controls, particularly with respect to intussusceptions.

Use of oral cholera vaccine in complex emergencies: what next? Summary report of an expert meeting and recommendations of WHO

Two meetings of the World Health Organization (WHO)-in 1999 and 2002-had examined the potential use of oral cholera vaccines (OCVs) as an additional public-health tool for the control of cholera. In the light of the work accomplished since 2002, WHO convened a third meeting to reexamine with a group of experts the role that OCVs might play in preventing potential outbreaks of cholera in crisis situations and to discuss the use of OCVs in endemic settings. The aim of the meeting was to agree a framework for the recommendations of WHO on these subjects and to consider the pertinence of further demonstration projects in endemic settings. The meeting addressed key issues, including currently-available vaccines, surveillance, and cholera-control measures in complex emergencies, and past experiences of using OCVs. More than 40 participants took part in the discussions, representing cholera-prone countries, humanitarian organizations, scientific institutions, United Nations agencies, and WHO. The experts agreed that when considering the use of OCVs in emergencies, a multidisciplinary approach is essential and that the prevention and control of cholera should be envisaged within the larger context of public-health priorities in times of crisis. As for the use of OCVs in endemic settings, all participants acknowledged that further data need to be collected before a clear definition of endemicity and potential vaccination strategies can be established. Results of further studies on the vaccines per se are also awaited. Recommendations relating to the use of OCVs (a) in complex emergencies and (b) in endemic settings were elaborated, and a decision-making tool for assessing the pertinence of use of OCVs in emergency settings was drafted. The document was finalized by an ad-hoc working group convened in Geneva on 1 March 2006 and is now available for field-testing. After testing, that should be carried out with the involvement of WHO and feedback from field partners, the decision-making tool will be adapted and disseminated.

Expression of foreign proteins in a Vibrio cholerae vaccine strain using the stationary phase hemagglutinin/protease promoter

The use of the hemagglutinin(HA)/protease promoter and secretion signals to drive expression and secretion of a foreign antigen in a live genetically attenuated cholera vaccine candidate is demonstrated. A Vibrio cholerae vaccine strain, containing a HA/protease-tetanus toxin C fragment (TCF) fusion, produced soluble-and cell-associated TCF. The fraction of TCF secreted to the culture medium was degraded unless expressed in a HA/protease-defective vaccine strain. Comparison of the hapA promoter with the strong Tac promoter using quantitative real time PCR revealed that at least five times more TCF mRNA was produced when expressed from the hapA promoter.