Randomized, double-blind placebo-controlled trial to evaluate the safety and immunogenicity of combined Salmonella typhi Ty21a and Vibrio cholerae CVD 103-HgR live oral vaccines

Cholera Vaccine: Recommendations of the Advisory Committee on Immunization Practices, 2022

This report summarizes all recommendations from CDC’s Advisory Committee on Immunization Practices (ACIP) for the use of lyophilized CVD 103-HgR vaccine (CVD 103-HgR) (Vaxchora, Emergent BioSolutions, Gaithersburg, MD) in the United States. The live attenuated oral cholera vaccine is derived from

Vibrio cholerae O1 and is administered in a single dose. Cholera is a toxin-mediated bacterial gastrointestinal illness caused by toxigenic V. cholerae serogroup O1 or, uncommonly, O139. Up to 10% of infections manifest as severe cholera (i.e., cholera gravis), profuse watery diarrhea that can cause severe dehydration and death within hours. Fluid replacement therapy can reduce the fatality rate to <1%. Risk factors for cholera gravis include high dose exposure, blood group O, increased gastric pH (e.g., from antacid therapy), and partial gastrectomy. Cholera is rare in the United States, but cases occur among travelers to countries where cholera is endemic or epidemic and associated with unsafe water and inadequate sanitation. Travelers might be at increased risk for poor outcomes from cholera if they cannot readily access medical services or if they have a medical condition that would be worsened by dehydration, such as cardiovascular or kidney disease. This report describes previously published ACIP recommendations about use of CVD 103-HgR for adults aged 18–64 years and introduces a new recommendation for use in children and adolescents aged 2–17 years. ACIP recommends CVD 103-HgR, the only cholera vaccine licensed for use in the United States, for prevention of cholera among travelers aged 2–64 years to an area with active cholera transmission. Health care providers can use these guidelines to develop the pretravel consultation for persons traveling to areas with active cholera transmission.

Update on CVD 103-HgR single-dose, live oral cholera vaccine

Cholera remains endemic in >50 countries, putting millions at risk, especially young children for whom killed vaccines offer limited protection. An oral, live attenuated vaccine - CVD 103-HgR (Vaxchora vaccine) - was licensed by the US FDA in 2016 for adults aged 18-64 years traveling to endemic regions, based on clinical trials in human volunteers showing the vaccine was well tolerated and conferred 90% efficacy within 10 days. The evidence base for Vaxchora vaccine has expanded with additional clinical trial data, in older adults (aged 46-64 years) and children (aged 2-17 years), demonstrating that the vaccine produces a strong vibriocidal antibody response. Over 68,000 doses have been administered in the United States, with no new safety signals. The dose volume has been reduced in children to improve acceptability, and cold chain requirements are less st ringent, at +2°C─+8°C. The vaccine has recently been licensed in the Untied States for children aged 2-17 years, in Europe for individuals aged ≥2 years, and for home administration in Europe. Next steps include a Phase 4 study in infants (6-23 months). Additional information is needed regarding duration of immunity, the need for and timing of revaccination, and efficacy data from lower-middle-income countries.

An overview of VaxchoraTM, a live attenuated oral cholera vaccine

Cholera remains a public health threat among the least privileged populations and regions affected by conflicts and natural disasters. Together with Water, Sanitation and Hygiene practices, use of oral cholera vaccines (OCVs) is a key tool to prevent cholera. Bivalent whole-cell killed OCVs have been extensively used worldwide and found effective in protecting populations against cholera in endemic and outbreak settings. No cholera vaccine had been available for United States (US) travelers at risk for decades until 2016 when CVD 103-HgR (Vaxchora™), an oral live attenuated vaccine, was licensed by the US FDA. A single dose of Vaxchora™ protected US volunteers against experimental challenge 10 days and 3 months after vaccination. However, use of Vaxchora™ poses several challenges in resource poor settings as it requires reconstitution, is age-restricted to 18 to 64 years, has no data in populations endemic for cholera, and faces challenges related to cold chain and cost.

Evidence for CVD 103-HgR as an effective single-dose oral cholera vaccine

We propose the ideal oral cholera vaccine (OCV) should be an inexpensive, single, oral dose that rapidly confers immunity for a long duration, and is well tolerated by individuals vulnerable to cholera. Vaccine trials in industrialized countries of a single oral dose of 5 × 108 colony forming units (CFU) of the live, attenuated cholera strain CVD 103-HgR have shown 88–97% serum vibriocidal antibody seroconversion rates, a correlate of protection and documented vaccine efficacy of ≥80% using volunteer challenge studies with wild-type cholera. For individuals of developing countries, a 5 × 109 CFU dose of CVD 103-HgR is necessary to elicit similar antibody responses. Presently, a reformulation of CVD 103-HgR is in late-stage clinical development for prospective US FDA licensure; making a cholera vaccine for US travelers potentially accessible in 2016. The availability of CVD 103-HgR should be a welcome addition to the currently available OCVs.

Vaccinal issues between Belgian and French travelers

INTRODUCTION

The yellow-fever vaccination center of the Tourcoing Hospital (France) has been accessible to Belgian travelers since its opening in 1994.

METHOD

The authors reported the specificities of these consultations during the year 2010, by retrospectively analyzing electronic medical records.

RESULTS

Some medical issues encountered during the consultation were due to differences in vaccination schedules: for the polio vaccine, since the last dose is administered between 5 and 7 years of age in Belgium; and for the measles vaccine since a late two-dose schedule (second dose between 12 and 13 years of age) is recommended in this country. Moreover, some specific vaccines are available only in Belgium: a diphtheria-tetanus bivalent vaccine, and a live attenuated oral typhoid vaccine.

DISCUSSION

The specificities of the Belgian border traveler consultation in our French yellow-fever center are due to a difference in European vaccination schedules; the physician must be aware of these.

CONCLUSION

The physician has to propose updates on vaccination schedules, and be aware of yellow-fever vaccine compatibility with vaccines recently administered in Belgium.

Oral vaccines for preventing cholera

EDITORIAL NOTE

This review is superseded by the published Cochrane Review, Saif‐Ur‐Rahman 2024 [https://doi.org/10.1002/14651858.CD014573], which considers only the oral killed vaccines because the live oral vaccines do not have World Health Organization (WHO) prequalification. Saif‐Ur‐Rahman 2024 also considered only currently available WHO pre‐qualified oral killed cholera vaccines (Dukoral, Shanchol, and Euvichol/Euvichol‐Plus).

BACKGROUND

Cholera is a cause of acute watery diarrhoea which can cause dehydration and death if not adequately treated. It usually occurs in epidemics, and is associated with poverty and poor sanitation. Effective, cheap, and easy to administer vaccines could help prevent epidemics.

OBJECTIVES

To assess the effectiveness and safety of oral cholera vaccines in preventing cases of cholera and deaths from cholera.

SEARCH STRATEGY

In October 2010, we searched the Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; the metaRegister of Controlled Trials (mRCT), and the WHO International Clinical Trials Registry Platform (ICTRP) for relevant published and ongoing trials.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of oral cholera vaccines in healthy adults and children.

DATA COLLECTION AND ANALYSIS

Each trial was assessed for eligibility and risk of bias by two authors working independently. Data was extracted by two independent reviewers and analysed using the Review Manager 5 software. Outcomes are reported as vaccine protective efficacy (VE) with 95% confidence intervals (CIs).

MAIN RESULTS

Seven large efficacy trials, four small artificial challenge studies, and twenty-nine safety trials contributed data to this review.Five variations of a killed whole cell vaccine have been evaluated in large scale efficacy trials (four trials, 249935 participants). The overall vaccine efficacy during the first year was 52% (95% CI 35% to 65%), and during the second year was 62% (95% CI 51% to 62%). Protective efficacy was lower in children aged less than 5 years; 38% (95% CI 20% to 53%) compared to older children and adults; 66% (95% CI 57% to 73%).One trial of a killed whole cell vaccine amongst military recruits demonstrated 86% protective efficacy (95% CI 37% to 97%) in a small epidemic occurring within 4 weeks of the 2-dose schedule (one trial, 1426 participants). Efficacy data is not available beyond two years for the currently available vaccine formulations, but based on data from older trials is unlikely to last beyond three years.The safety data available on killed whole cell vaccines have not demonstrated any clinically significant increase in adverse events compared to placebo.Only one live attenuated vaccine has reached Phase III clinical evaluation and was not effective (one trial, 67508 participants). Two new candidate live attenuated vaccines have demonstrated clinical effectiveness in small artificial challenge studies, but are still in development.

AUTHORS' CONCLUSIONS

The currently available oral killed whole cell vaccines can prevent 50 to 60% of cholera episodes during the first two years after the primary vaccination schedule. The impact and cost-effectiveness of adopting oral cholera vaccines into the routine vaccination schedule of endemic countries will depend on the prevalence of cholera, the frequency of epidemics, and access to basic services providing rapid rehydration therapy.

Vaccines administered simultaneously: directions for new combination vaccines based on an historical review of the literature

OBJECTIVES

The recognized benefits of administering vaccines simultaneously has encouraged vaccine producers to develop combination vaccines. If contemporary research and development can realize vaccines that achieve the current standards for safety, immunogenicity, and efficacy, other specific vaccine associations may also merit reconsideration as combination vaccines.

METHODS

An historical review of the vaccine association literature reveals two important themes: first, the programs of mass vaccination, in particular, the eradication of smallpox, sessions where multiple vaccines (other than the smallpox vaccine) were given concurrently, and the Expanded Programme on Immunization (EPI); and, second, the domain of travel vaccines, including travellers to a disease-endemic country (such as migrants, tourists, military personnel, or expatriates) and WHO requirements for international travellers.

RESULTS/CONCLUSIONS

Based on this historical review, combination vaccines worth reconsideration could fill epidemiologic niches in the EPI with, for instance, a measles--yellow fever, a measles--Japanese encephalitis or a pertussis-based paediatric combination rabies vaccine. Furthermore, other combinations could broaden protection against the pathogens responsible for meningitis, pneumonia, or enteric diseases. Nevertheless, complex issues such as necessity, feasibility, or affordability will ultimately determine if any one of these becomes a combination vaccine.

Salmonella vaccines for use in humans: present and future perspectives

In recent years there has been significant progress in the development of attenuated Salmonella enterica serovar Typhi strains as candidate typhoid fever vaccines. In clinical trials these vaccines have been shown to be well tolerated and immunogenic. For example, the attenuated S. enterica var. Typhi strains CVD 908-htrA (aroC aroD htrA), Ty800 (phoP phoQ) and chi4073 (cya crp cdt) are all promising candidate typhoid vaccines. In addition, clinical trials have demonstrated that S. enterica var. Typhi vaccines expressing heterologous antigens, such as the tetanus toxin fragment C, can induce immunity to the expressed antigens in human volunteers. In many cases, the problems associated with expression of antigens in Salmonella have been successfully addressed and the future of Salmonella vaccine development is very promising.

Local and systemic immune responses to combined vibrio cholerae CVD103-HgR and salmonella typhi ty21a live oral vaccines after primary immunization and reimmunization

The local and systemic antibody responses elicited following concomitant primary immunization and reimmunization with the live oral attenuated Vibrio cholerae CVD103-HgR and Salmonella typhi Ty21a vaccine strains were determined in healthy adult volunteers. A more pronounced serum vibriocidal antibody response was generated after primary immunization compared to reimmunization 2.5 or 3.5 yr later. The seroconversion rate (> or =4-fold rise over baseline) was 81% subsequent to primary immunization versus 57% (p=0.018) and 65% (p=0.639) upon reimmunization at 2.5 and 3.5 yr, respectively. A similar trend was observed for serum anti-S. typhi lipopolysaccharide (LPS) antibodies. After primary immunization, 48% of subjects manifested a significant rise in coproantibody levels to V. cholerae LPS while 60% did so for cholera toxin (CT). Upon reimmunization, the response rate for LPS ranged from 38% at 2.5 yr to 56% at 3.5 yr (p>0.05), while that for CT varied from 31% (p=0. 007) to 50% (p=0.541) at 2.5 and 3.5 yr, respectively. The anti-S. typhi IgA coproantibody response rate was 70% subsequent to primary immunization versus 47% at 2.5 yr (p=0.021) and 63% at 3.5 yr (p=0. 77).

Bivalent cholera and typhoid vaccine

The live attenuated vaccine strains Vibrio cholerae CVD 103-HgR and Salmonella typhi Ty21a can be combined into an oral bivalent vaccine without compromising the immunogenicity of the individual vaccine strains. Seroconversion rates of 87 to 94% for Inaba vibriocidal antibodies and 72 to 91% for anti-S. typhi lipopolysaccharide antibodies (IgG or IgA) were reported in healthy European volunteers receiving a bivalent CVD 103-HgR/Ty21a vaccine-based schedule (bivalent vaccine on day 1 and monovalent Ty21a vaccine on days 3 and 5). The immunogenicity of bivalent CVD 103-HgR/Ty21a vaccine is not adversely affected by concomitant administration of mefloquine, yellow fever vaccine or oral polio vaccine. Chloroquine may reduce the immunogenicity of the CVD 103-HgR component and proguanil may reduce the immunogenicity of the Ty21a component. Bivalent CVD 103-HgR/Ty21a vaccine does not adversely affect the immunogenicity of the yellow fever YF 17D vaccine. The type, incidence and severity of adverse events seen in individuals receiving bivalent CVD 103-HgR/Ty21a vaccine-based schedules are similar to those that occur with the monovalent vaccines.

Immunizations for international travel

Immunization recommendations for international travelers is a complex subject that takes into consideration the geographic destination, planned activities during travel, health conditions at destination, length of trip, and underlying health status of the traveler. The final immunization program is also determined by how much time is available before departure and the worldwide availability of vaccines and their cost. In some cases, preventive behaviors and chemoprophylaxis may protect against the risk of infection when immunizations are unavailable or unobtainable.

Immunizations and travel

Determining the appropriate immunizations for international travelers is a complex, multifaceted process. This article proposes a stepwise and systematic approach to the immunization needs of the traveler-patient. Vaccines for routine health maintenance as well as special issues of the elderly, pregnant, immunocompromised, and child are important in the initial evaluation. Specific travel immunizations (i.e., those for routine travel, those required by a country, those that are geographically indicated and immunizations for extended stays) comprise the remainder of the immunization interview. Health care providers should also be familiar with cost and risk statistics, both the risk of the traveler contracting an illness overseas and the risk of side effects from the vaccines themselves. With such cost-benefit analysis, the provider can offer the traveler immunizations as well as information.