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.

Long-Term Immunogenicity of Live Oral Cholera Vaccine CVD 103-HgR in Adolescents Aged 12-17 Years in the United States

As part of a phase 4, randomized, double-blind, placebo-controlled trial to assess the immunogenicity and safety of PXVX0200 in children and adolescents aged 2-17 years, a subset of 73 adolescent subjects aged 12-17 years was followed for 2 years after vaccination and had blood collected for antibody assays on days 1, 11, 29, 91, 181, 365, 547, and 730. Endpoints included serum vibriocidal antibody (SVA) seroconversion, defined as a 4-fold or greater rise in antibody titer over baseline; geometric mean titers (GMTs); and geometric mean fold increase (GMFI) over baseline. Serum vibriocidal antibody seroconversion persisted in most subjects, with a rate of 64.5% noted at day 730. Geometric mean titers and GMFI both peaked at day 11 and remained greater than baseline at all time points, including day 730. Vaccination with PXVX0200 produces an immune response which persists for at least 2 years in adolescents aged 12-17 years.

Safety and Immunogenicity of Live Oral Cholera Vaccine CVD 103-HgR in Children and Adolescents Aged 6-17 Years

The attenuated recombinant Vibrio cholerae O1 vaccine strain CVD 103-HgR, redeveloped as PXVX0200, elicits a rapid serum vibriocidal antibody (SVA) response and protects against cholera-induced diarrhea in adult volunteer challenge trials but has not been studied in children in developed countries. We performed a phase 4, placebo-controlled, double-blind, multicenter study to assess the safety, immunogenicity, and tolerability of a single, oral dose of PXVX0200 in children and adolescents aged 6-17 years in the United States and bridged immunogenicity to adults aged 18-45 years from a separate lot consistency study. Volunteers were randomized to receive a single dose of 1 × 109 colony forming units (CFU) of PXVX0200 or placebo. Immunogenicity endpoints included SVA levels on days 1, 11, and 29 in volunteers aged 6-17 years and also on days 91 and 181 in volunteers aged 12-17 years. Safety was assessed by comparing solicited signs and symptoms on days 1-8, unsolicited adverse events (AEs) through day 29, and serious AEs through day 181. A total of 374 participants were enrolled, comprising 321 vaccine and 53 placebo recipients. The SVA seroconversion rates 10 days after immunization were 98.6% and 2.1% in vaccine and placebo recipients, respectively, and the vaccine seroconversion rate was non-inferior to the 93.5% rate seen in adults aged 18-45 years. Most reactogenicity was mild to moderate, and there were no vaccine-related serious AEs. The complete dose was consumed in 95.3% and 98.1% of vaccine and placebo recipients, respectively. PXVX0200 appears safe, immunogenic, and well tolerated in children and adolescents aged 6-17 years.

Cholera in travellers: a systematic review

Exposure to cholera is a risk for individuals and groups travelling to endemic areas, and the bacteria can be imported to cholera-free countries by returning travellers. This systematic review of the literature describes the circumstances in which cholera infection can occur in travellers and considers the possible value of the cholera vaccine for prevention in travellers. PubMed and EMBASE were searched for case reports of cholera or diarrhoea among travellers, with date limits of 1 January 1990-30 April 2018. Search results were screened to exclude the following articles: diarrhoea not caused by cholera, cholera in animals, intentional cholera infection in humans, non-English articles and publications on epidemics that did not report clinical details of individual cases and publications of cases pre-dating 1990. Articles were reviewed through descriptive analytic methods and information summarized. We identified 156 cases of cholera imported as a consequence of travel, and these were reviewed for type of traveller, source country, serogroup of cholera, treatment and outcomes. The case reports retrieved in the search did not report consistent levels of detail, making it difficult to synthesize data across reports and draw firm conclusions from the data. This clinical review sheds light on the paucity of actionable published data regarding the risk of cholera in travellers and identifies a number of gaps that should drive additional effort. Further information is needed to better inform evidence-based disease prevention strategies, including vaccination for travellers visiting areas of cholera risk. Modifications to current vaccination recommendations to include or exclude current or additional traveller populations may be considered as additional risk data become available. The protocol for this systematic review is registered with PROSPERO (registration number: 122797).

Safety and immunogenicity of single-dose live oral cholera vaccine strain CVD 103-HgR in healthy adults age 18-45

The attenuated recombinant Vibrio cholerae O1 vaccine strain CVD 103-HgR, re-developed as PXVX0200, elicits a rapid serum vibriocidal antibody (SVA) response and protects against cholera diarrhea in volunteer challenge studies. We performed a phase 3, placebo controlled, double blind, multi-center study to further assess the safety, immunogenicity, and lot-to-lot consistency of PXVX0200. Adult volunteers 18-45 years of age were randomized 8:1 to receive a single dose of 1 × 10⁹ CFU of PXVX0200 from three production lots or saline placebo. Immunogenicity endpoints included SVA and anti-cholera toxin (CT) antibody levels on days 1, 11, 29, 91 and 181. Safety was assessed by comparing solicited signs and symptoms on days 1-8, unsolicited adverse events through day 29 and serious adverse events through day 181. A total of 3146 participants were enrolled, including 2795 vaccine and 351 placebo recipients. The SVA seroconversion rates at day 11 were 94% and 4% in the PXVX0200 and placebo recipients, respectively (P < .0001). Cumulative SVA seroconversion occurred among 96% of vaccine recipients. PXVX0200 SVA GMTs peaked on day 11 and remained significantly higher than placebo through day 181 while the fold-rise over baseline in PXVX0200 anti-CT antibody was significantly greater than placebo at every post-vaccination time point. Most reactogenicity was mild and resolved within 1-3 days with headache and diarrhea more frequently reported in PXVX0200 recipients. There were no differences in unsolicited adverse events and no study-related serious adverse events. Immunogenicity and safety endpoints were equivalent between the three production lots. PXVX0200 is immunogenic and well tolerated across multiple production lots.

CLINICAL TRIALS REGISTRATION

Clinicaltrials.gov NCT02094586.

Imported cholera with acute renal failure after a short business-trip to the Philippines, Germany, October 2015

A German businessman developed acute watery diarrhoea after a three-day trip to the Philippines. He was admitted with severe hypotension and acute renal failure, but recovered with rapid rehydration. Vibrio cholerae O1 serotype Ogawa was isolated. Physicians need to be aware of endemic cholera in Asia including the Philippines and consider this in their pre-travel advice.

Widespread epidemic cholera caused by a restricted subset of Vibrio cholerae clones

Since 1817, seven cholera pandemics have plagued humankind. As the causative agent, Vibrio cholerae, is autochthonous in the aquatic ecosystem and some studies have revealed links between outbreaks and fluctuations in climatic and aquatic conditions, it has been widely assumed that cholera epidemics are triggered by environmental factors that promote the growth of local bacterial reservoirs. However, mounting epidemiological findings and genome sequence analysis of clinical isolates have indicated that epidemics are largely unassociated with most of the V. cholerae strains in aquatic ecosystems. Instead, only a specific subset of V. cholerae El Tor 'types' appears to be responsible for current epidemics. A recent report examining the evolution of a variety of V. cholerae strains indicates that the current pandemic is monophyletic and originated from a single ancestral clone that has spread globally in successive waves. In this review, we examine the clonal nature of the disease, with the example of the recent history of cholera in the Americas. Epidemiological data and genome sequence-based analysis of V. cholerae isolates demonstrate that the cholera epidemics of the 1990s in South America were triggered by the importation of a pathogenic V. cholerae strain that gradually spread throughout the region until local outbreaks ceased in 2001. Latin America remained almost unaffected by the disease until a new toxigenic V. cholerae clone was imported into Haiti in 2010. Overall, cholera appears to be largely caused by a subset of specific V. cholerae clones rather than by the vast diversity of V. cholerae strains in the environment.