Abstract: The current pandemic of cholera is caused primarily by Vibrio cholerae O1 of the El Tor biotype. Live attenuated classical biotype V. cholerae vaccine strains prevent severe and moderate cholera due to either biotype in challenged volunteers but may provide less protection against mild cholera due to El Tor organisms. CVD 110, a new ctxA-deleted vaccine strain derived from an El Tor Ogawa parent, lacks zona occludens toxin (Zot), accessory cholera enterotoxin (Ace), and hemolysin/enterotoxin. Ten healthy adult volunteers were given 10(8) cfu of CVD 110 with buffer; 7 developed diarrhea (mean stool volume, 861 mL). Vaccine organisms were shed in stool by all vaccines and were recovered from duodenal fluid in three-quarters of vaccinees. After vaccination, the geometric mean peak reciprocal vibriocidal titer among vaccinees was 17,829. CVD 110 is a powerful immunogen but insufficiently attenuated despite the absence of known potential enterotoxins of V. cholerae. Another unrecognized toxin or colonization alone may be responsible for diarrhea after ingestion of this strain.

Abstract: To investigate the importance of vitamin A in the ability to respond to oral antigen administration, rats were fed a vitamin A-free diet. The animals were immunized perorally three times with a mixture of cholera toxin (CT) and a commercial cholera vaccine. The total immunoglobulin A (IgA) concentration as well as the specific IgA anti-CT antibody levels in serum and bile was significantly lower in the vitamin A-deficient animals than in the paired fed controls (animals that were fed a normal commercial diet in an amount equal to the amount the deficient animals consumed), while the levels of total and specific anti-CT IgG were not affected to the same extent by the vitamin A deficiency. The number of IgA anti-CT antibody-producing cells in the mesenteric lymph nodes after immunization was also significantly lower in the vitamin A-deficient rats than in the control rats. Supplementation of the diet with retinyl palmitate restored the ability to mount an IgA antibody response to the antigen, since the level of specific IgA anti-CT antibodies in relation to the total IgA concentration was as high in the vitamin A-supplemented group as in the paired fed control group. Restricted diet intake by itself did not affect the ability to respond adequately to the antigen since there was no difference in IgA anti-CT antibody level between paired fed rats and those being fed ad libitum. Assessment of transforming growth factor beta in cell cultures revealed no difference between vitamin A-deficient and paired fed animals. In summary, vitamin A deficiency resulted in a decreased number of IgA-producing cells, decreased IgA production, and a reduced ability to respond with IgA antibodies to the oral cholera vaccine.

Abstract: A newly formulated, oral, inactivated whole cell plus recombinant B subunit (WC/rBS) cholera vaccine was evaluated in US military personnel. In the first study, 74 subjects were given two doses 14 days apart. In the second study, 186 subjects were randomized into four groups; two groups received vaccine with either full (4 g) or half (2 g) strength bicarbonate buffer, and two groups received either full or half strength buffer without vaccine. Mild gastrointestinal symptoms were associated with full buffer (P = .02) but not with the vaccine. In the first study, 36% of all subjects and 55% with low prevaccination titers ( or = 2-fold rise in vibriocidal antibody level; > 80% of subjects developed a 4-fold rise in anti-cholera toxin (CT) titers. Post-vaccination IgA and IgG anti-CT titers were approximately 1.5-fold higher among persons receiving full strength buffer (P = .05). The WC/rBS vaccine is safe and immunogenic in North Americans, although some mild gastrointestinal symptoms occur with the high concentration of buffer necessary to protect the B subunit from gastric acid denaturation. Prior immunity to cholera conferred by parenteral vaccine decreased vibriocidal antibody response.

Abstract: Peripheral blood immunoglobulin A antibody-secreting-cell (ASC) responses are thought to reflect the mucosal immune response to locally presented antigens. We evaluated the ASC response to cholera toxin (CT) and Inaba lipopolysaccharide (LPS) in 26 North American volunteers following immunization with a single oral dose of live attenuated Vibrio cholerae O1 vaccine strain CVD 103-HgR and again upon homologous wild-type challenge with V. cholerae classical Inaba 569B. Challenge occurred at either 7, 30, or 180 days after vaccination. The CT and LPS ASC responses of volunteers following vaccination (83 and 55%, respectively) were similar in magnitude and frequency to those of unvaccinated controls following wild-type challenge (80 and 60%, respectively [0.1 < or = P < or = 0.9]). The responses were primarily immunoglobulin A. Vaccinated volunteers challenged within 30 days of vaccination had reduced or nondetectable CT and LPS ASC responses. Challenge at 6 months resulted in a heightened ASC response to LPS, confirming the existence of mucosal memory. ASC responses to CT upon challenge at 6 months were detectable but not different from that seen following primary immunization, suggesting that secondary ASC responses to different antigens from a single vaccine operate independently. In spite of these variable ASC responses, the vaccine efficacy was 100% following challenge for all vaccinees. V. cholerae-specific ASC responses following antigenic reexposure gave information on the presence of mucosal B memory cells but did not correlate with protective immunity. As such, these ASC assays will have limited usefulness for evaluating vaccine responders in vaccine field trials in cholera-endemic areas where prior V. cholerae O1 exposure is unknown.

Abstract: The recent spread of cholera to Latin America, together with the persistent burden of this disease in Asia and Africa, have stimulated efforts to evaluate new cholera vaccines in field settings. Although the standard experimental paradigm for vaccine field trials is well established, the success of these trials will also depend on suitable consideration of the epidemiology of cholera and of cholera vaccination in the setting under study. Epidemiological studies done in Bangladesh emphasize the importance of appreciating the poorly predictable, multifocal occurrence of cholera in estimating a probable incidence of cholera for a field trial. They also underscore how the filtering effect of enrolling subjects into a prospective trial can dramatically reduce the available population for study, and can yield a study sample whose expected risk of cholera differs markedly from that for the source population. Finally, the data highlight the subtle effects that the mode of surveillance and the choice of an outcome definition can have upon protective efficacy, and emphasize the need for subgroup analyses that address the distinctive variations in vaccine protection that may occur in subjects differing in age and in ABO blood groups, and in subjects exposed to classical versus El Tor cholera.

Abstract: In a randomized, placebo-controlled field trial of B subunit-killed whole cell (BS-WC) and killed whole cell only (WC) inactivated oral cholera vaccines in rural Bangladesh, active surveillance of selected neighborhoods during the first year after vaccination identified 127 Vibrio cholerae O1 infections among 3285 three-dose recipients. For each vaccine, protective efficacy was greater against symptomatic (57%, P < .05 for BS-WC; 58%, P < .05 for WC) than against asymptomatic infections (46%, P < .05 for BS-WC; 32%, P = .09 for WC), and protection against each grade of infection was demonstrable for both the classical and El Tor biotypes. Although vaccine protection against symptomatic infections was evident in both young children and older persons, only persons vaccinated at age > 5 years were protected against asymptomatic infections. These results suggest that the inactivated oral vaccines acted both to protect against intestinal colonization by V. cholerae O1 and to interrupt the pathogenic sequence of established infections.

Abstract: The authors conducted a two-period crossover study of the reactogenicity and immunogenicity of live oral cholera vaccine CVD 103-HgR among US university students. Subjects ingested 5 x 10(8) colony forming units of either killed Escherichia coli K12 placebo or vaccine, followed by the opposite treatment one week later. Surprisingly, the dynamics of the immunologic response were influenced by prior ingestion of placebo. Subjects who received placebo first showed stronger vibriocidal antibody responses 2 weeks after vaccination compared with subjects who received vaccine first; this same pattern was seen for antitoxin titers. The authors suggest that ingestion of E. coli K12 one week prior to immunization boosts the immunologic response to vaccine by an unknown mechanism. Future crossover studies that examine immunologic outcomes might be designed to explore the ubiquity of such an effect.

Abstract: A vaccine formulation comprising conjugates of detoxified LPS with proteins including cholera toxin (CT) is disclosed. Treatment with hydrazine (DeA-LPS) reduces the endotoxic properties of the LPS to clinically acceptable levels and results in a larger and more antigenic molecule than the saccharide produced by acid hydrolysis. The conjugates utilizing the cholera toxin of V. cholerae are disclosed which have low levels of pyrogen, no toxic activity upon Chinese hamster overay cells and elicit booster responses of vibriocidal and CT antibodies when injected subcutaneously as saline solutions into mice. The conjugates produced as a cholera vaccine induce the same antibodies as parenterally injected cellular vaccines but have improved safety and immunologic properties.

Abstract: Parenteral immunization with either formalin-fixed whole cells of the fimbriate Bgd17 strain or purified fimbriae protected against Vibrio cholerae O1 infection in rabbits, independent of biotype and serotype. Parenteral immunization of adult rabbits with purified fimbriae prior to V. cholerae O1 challenge resulted in a reduction of 2 to 3 orders of magnitude in the number of bacteria recovered from the small intestines of immunized rabbits in comparison to non-immunized controls. IgG and IgA antibodies against fimbrillin of V. cholerae O1 were detected in the convalescent sera of patients with cholera; however, little fimbrial antigen was detected in the commercially available cholera vaccines when examined by polyclonal and monoclonal antibodies against fimbriae. These data suggest that fimbrial hemagglutinin is a major adhesin of V. cholerae O1 and that parenteral immunization with fimbriae generates a specific immune response in the gut that may serve as one means of mitigating subsequent V. cholerae O1 gut infection.

Abstract: The invention features a nontoxigenic genetically stable mutant strain of V. cholerae which lacks any functional attRS1 sequences is useful as a live, oral vaccine for inducing immunological protection against cholera and a method for making same. The invention also features a killed, oral cholera vaccine comprising at least a first and a second V. cholerae strain, wherein at least one of the strains is a different serotype, and the vaccine also contains cholera toxin B subunit, produced by at least one of the serotypes.

Abstract: The current pandemic of cholera coincides with a flurry of research activities in cholera prevention and cure. This article highlights important developments in cholera research, including key findings of a large-scale oral cholera vaccine trial, new insights in cholera epidemiology and risk factors, and recent directions in rehydration therapy and medical treatment of cholera.

Abstract: Considerable progress has been made in the last decade in developing vaccines against the enteric infections of greatest public health importance. A quadrivalent rotavirus vaccine consisting of rhesus rotavirus vaccine (which contains serotype 3 neutralization antigen) and three reassortant viruses (rhesus virus expressing neutralization antigens of serotypes 1, 2 or 4) is undergoing placebo-controlled field trials of efficacy in the USA and in two developing countries. Two new vaccines against typhoid fever (oral Ty21a and parenteral Vi polysaccharide) have been licensed in many countries. Even newer generations of typhoid vaccines are undergoing clinical testing, including new attenuated S. typhi strains and Vi polysaccharide-carrier protein conjugate vaccines. Two inactivated oral cholera vaccines, consisting of inactivated V. cholerae 01 bacteria alone or in combination with purified B subunit of cholera toxin, each conferred 50–53% protection over 3 years in a field trial in Bangladesh where subjects were immunized with a three-dose regimen. In extensive clinical trials in adults and children in less-developed countries, an engineered live oral cholera vaccine, strain CVD 103-HgR, has been shown to be well tolerated and highly immunogenic following administration of just a single oral dose; a large-scale field trial in 70000 subjects is underway to investigate the efficacy of this vaccine. Several candidate vaccines against Shigella and enterotoxigenic Escherichia coli are in clinical trials. Accumulating knowledge on pathogenesis of enteric infections and advances in mucosal and cellular immunology, coupled with the application of modern biotechnology, have resulted in a plethora of vaccine candidates. It is expected that in future years efforts will be directed to construct vaccines against other enteric pathogens.

Abstract: Cholera vibrios can be allocated to one of three biotypes (classical, intermediate and El Tor), each of which can be sub-divided into two serotypes (Ogawa and Inaba). Vibriocidal tests with absorbed antisera have shown no evidence of biotype specificity in the killing of bacteria, but they have confirmed the role of the two serotype-specific antigens in immunity to cholera. The same presence of serotype specificity, and absence of biotype specificity, has been found by bacterial agglutination, an easier and quicker serological test. The use of this simpler test in ensuring a balanced serotype response to cholera vaccine is discussed, together with evidence that may lead to the production of more effective vaccine and better immunity.

Abstract: The reactogenicity and immunological effectiveness of different doses of cholera vaccine for oral administration (in tablets), containing choleragen toxoid, Ogawa and Inaba O-antigens and some of Vibrio cholerae exoenzymes, have been tested on 143 children aged 2-17 years. In this investigation the optimum immunization doses of the preparation have been established: two tablets containing 100,000 binding units (BU) of the toxoid and 2,500 units of O-antigen for children 11-14 years; four tablets containing 200,000 BU of the toxoid and 5,000 units of O-antigen for adolescents aged 15-17 years. An essential advantage of the oral vaccine over vaccines intended for parenteral administration lies in its capacity for inducing the accumulation of secretory antibodies (coproantibodies) in practically all vaccinees.

Abstract: Considerable progress has been made in the last decade in developing vaccines against the most important bacterial enteric infections. Two new vaccines against typhoid fever (oral Ty21a and parenteral Vi polysaccharide) have been licensed in many countries. Newer generations of more sophisticated typhoid vaccines are undergoing clinical testing including recombinant attenuated S typhi strains and Vi polysaccharide-carrier protein conjugate vaccines. Two inactivated oral cholera vaccines, consisting of inactivated V cholerae 01 bacteria alone or in combination with the B subunit of cholera toxin, each conferred 50% to 53% protection over 3 years in a field trial in Bangladesh where subjects were immunized with a three-dose regimen. An engineered live oral cholera vaccine, strain CVD 103-HgR, has been shown in extensive clinical trials to be well tolerated by children and adults in developing countries and highly immunogenic following administration of just a single oral dose; a large-scale field trial of the efficacy of this vaccine is underway. Several candidate vaccines against Shigella and enterotoxigenic E coli are in clinical trials.

Abstract: A live attenuated oral cholera vaccine (CVD 103-HgR) was given to 434 travelers in February and August of 1993. Results from 277 returned questionnaires show that the oral vaccine was tolerated well. 110 of the returned questionnaires were from people who had received oral vaccine alone. 167 were from people who were given the oral vaccine and 1 or more parenteral vaccines. 21% (26/110) of the first group reported adverse effects while 32% (53/167) of the second group did so. Diarrhea nausea and abdominal cramps which were not common effects of the parenteral vaccine were mild and nondebilitating; however the incidence of gastrointestinal effects was higher than in previous studies. This new vaccine does not provide protection against Bengal cholera (non-01 strain Vibrio cholerae 0139).

Abstract: More than 80% of all the worlds children have been covered by immunization. The scientific community must expand the range of communicable diseases covered by immunization programs and streamline vaccination procedures. Trans-disease vaccinology is a new immunology specialty aimed at improving vaccine efficiency and streamlining vaccine delivery systems. Genetic engineering is used to develop vaccines consisting of very attenuated harmless viruses or bacteria to transport antigens from a pathogen into the body. For example scientists can affix a gene or picked of DNA from a malaria parasite onto the cowpox virus. When the modified virus divides it makes the malarial protein. Engineering can also combine several key genes thus attacking the malaria parasite from different fronts. Another area of trans-disease vaccinology is incorporation of at least 1 gene designed to enhance the immune response in a transplanted gene package. For example scientists can transplant interleukin genes and vaccine genes into a live virus vector to induce immunity in animals with a weakened immune system. This type of vaccine would be helpful in countries with widespread malnutrition. Research in a single-shot vaccination involves controlling the release of antigens after injection thereby eliminating the need for a booster shot. Research needs to examine ways to invoke the immune response where it is most needed e.g. a cholera vaccine should target the intestines. WHO/UND Development Programme (UNDP) is testing group B and group A/C meningococcal vaccines to fight meningitis epidemics new measles vaccines for early infancy vaccines for diarrheal diseases and improved tuberculosis vaccines WHO/UNDP/WB coordinates research in vaccines for malaria and schistosomiasis. Various clinical trials of AIDS vaccines are underway. The leading obstacles for many pathogens is that they are capable of mutation and variation resulting in dodging immune defenses. The Childrens Vaccine Initiative centers on research and development.

Abstract: Perspectives of cholera vaccines with emphasis in their possible usage in Latin American countries are discussed. Microbiology, antigenicity, relevant aspects of traditional serology, protective immune responses and epidemiological data up to December, 1991, are presented. Indications of parenteral vaccines are discussed. Finally, perspectives of usage of cholera vaccines in Latin America are analyzed.

Abstract: Dr. Peters review of childhood immunizations in the US (Dec. 17 issue) mentions policies that differ from those of the WHO especially with respect to immunization against cholera and poliomyelitis. We wish to clarify these differences. The WHO does not recommend cholera vaccine for travelers and no country requires it for entry. The only available cholera vaccine is of low efficacy and provides at best only short-term immunity. Immunization against cholera may impart a false sense of security making travelers less likely to use more effective protective measures. The safety of poliovirus vaccine is frequently questioned in patients infected with the human immunodeficiency virus (HIV). Oral poliovirus vaccine is a live-virus vaccine raising concerns about an increased risk of vaccine-associated poliomyelitis in HIV-infected recipients and their contacts. In 1987 the WHO and the UN Childrens Fund stated that in countries in which poliomyelitis is endemic the benefits of oral poliovirus vaccine outweighed the apparently low risk of adverse events in the presence of HIV infection. In countries such as Rwanda and Zaire prospective studies of cohorts of children born to HIV-infected women and immunized with oral poliovirus vaccine in infancy have not shown an increased risk of any side effect of the vaccine. Therefore for countries in which poliomyelitis is endemic the WHO continues to recommend giving infants four doses of oral poliovirus vaccine before the age of 12 months regardless of the possible presence of HIV infection. On the basis of data available to the WHO in January 1993 no case of vaccine-associated poliomyelitis has been reported in an HIV-infected recipient or contact. However vigilance should be maintained and any case of poliomyelitis in an HIV-infected person should be reported to the WHO. (full text)

Abstract: Pasteur cholera vaccine consists of isolated antigenic fractions from V. cholerae El Tor Ogawa and Inaba. Enteric coated microgranules were prepared from antigen lyophilisate. Three doses of this vaccine were administered orally to 19 healthy young Thai adults at one week intervals. None of the volunteers experienced untowards reactions. The vibriocidal antibody responses manifested a significant antibody rise (> 4 fold) to serovar Inaba in 8 vaccinees (42.1%) and Ogawa in 4 (21 .I%). Five and 6 vac- cinees (26.3% and 31.6'%) showed a 24 fold rise of IgG and IgA anti-LPS, respectively.

Abstract: Recombinant A-B+ Vibrio cholerae O1 strain CVD 103-HgR is a safe, highly immunogenic, single-dose live oral vaccine in adults in industrialized countries. Safety, excretion, immunogenicity, vaccine transmissibility, and environmental introduction of CVD 103-HgR were investigated among 24- to 59-month-old children in Jakarta. In 81 households, 1 child was randomly allocated a single dose of vaccine (5 x 10(9) cfu) and another, placebo. Additionally, 139 unpaired children were randomly allocated vaccine or placebo. During 9 days of follow-up, diarrhea or vomiting did not occur more often among vaccines than controls. Vaccine was minimally excreted and was isolated from no controls and from 1 (0.6%) of 177 unvaccinated family contacts. A 4-fold or higher rise in serum vibriocidal antibody was observed in 75% of vaccines (10-fold rise in geometric mean titer over baseline). Of 135 paired placebo recipients or household contacts, 5 had vibriocidal seroconversions. Moore swabs placed in sewers and latrines near 97 households failed to detect vaccine. These observations pave the way for a large-scale field trial of efficacy.