CD4+ T-cell responses to an oral inactivated cholera vaccine in young children in a cholera endemic country and the enhancing effect of zinc supplementation

Immunization of young children with the oral inactivated whole cell cholera vaccine Dukoral^® containing recombinant cholera toxin B subunit (CTB) induces antibody responses which can be further enhanced by zinc supplementation. We have investigated if immunization with the cholera vaccine induces specific T-cell responses in young children and also whether zinc supplementation influences these responses. Bangladeshi children (10–18 months old) received vaccine alone, vaccine together with zinc supplementation or only zinc. T-cell blast formation indicating a proliferative response was analyzed by the flow cytometric assay of cell-mediated immune response in activated whole blood (FASCIA) and cytokines were measured by ELISA. Stronger T-cell responses were detected if a modified CTB molecule (mCTB) with reduced binding to GM1 ganglioside was used for cell stimulation compared to normal CTB. After vaccination, CD4+ T cells responded to mCTB with significantly increased blast formation (P < 0.01) and IFN-γ production (P < 0.05) compared to before vaccination. No responses to mCTB were detected in children receiving zinc alone (P > 0.05). The IFN-γ production was significantly higher (P < 0.01) but the blast formation comparable (P > 0.05) in children receiving zinc plus vaccine compared to in children receiving vaccine alone. The vibriocidal antibody responses induced by the vaccine were also significantly higher in children receiving zinc supplementation (P < 0.001). Our results thus show that oral cholera vaccination induces a Th1 T-cell response in young children, and that the IFN-γ as well as the vibriocidal antibody responses can be enhanced by zinc supplementation.     

Investigations into the safety and immunogenicity of a killed oral cholera vaccine developed in Viet Nam

OBJECTIVE: To evaluate a killed oral cholera vaccine produced in Viet Nam, and to compare the Vietnamese vaccine with one that is licensed internationally. METHOD: Two-dose regimens of a locally produced, bivalent, anti-O1, anti-O139 killed oral whole-cell cholera vaccine (biv-WC) and of a commercially available, monovalent (anti-O1) oral recombinant B subunit-killed whole-cell cholera vaccine (rBS-WC) were compared in two trials in Viet Nam. In the first trial, 144 adults were randomized to biv-WC with or without buffer, rBS-WC with buffer, or placebo without buffer. In the second, 103 children aged 1-12 years were randomized to biv-WC without buffer, rBS-WC with buffer, or placebo without buffer. FINDINGS: No regimen was associated with significant side-effects. In adults, ca 60% of recipients of either vaccine exhibited at least fourfold serum anti-O1 vibriocidal antibody responses and ca 40% of recipients of biv-WC demonstrated anti-O139 vibriocidal responses. Both anti-O1 (ca 90% in each vaccine groupand anti-O139 (68% in the biv-WC group) vibriocidal responses occurred more frequently in children. The responses to biv-WC were unaffected by the receipt of buffer. CONCLUSION: It was concluded that biv-WC was safe and immunogenic, that it could be administered without buffer, and that it could elicit robust immune responses even in children, for whom the risk of endemic cholera is highest.     

Report of the 1966-67 cholera vaccine trial in rural East Pakistan

A controlled cholera vaccine field trial was carried out in rural East Pakistan to determine the efficacy of a cholera vaccine of average antigenic potency when used in a continuing programme with annual reimmunizations. A cohort of 40 000 children aged 0-14 years was equally divided into a control group and 3 vaccine groups. Inoculations of vaccine were given annually for 3 years just before the start of the cholera season, and follow-up continued for 2 additional years. The results indicate that there was increasing protection with reimmunization, reaching a maximum with 3 doses. One dose produced 43% protection, 2 doses 64%, 3 doses 81%, and 4 doses 76%. Protection was more sustained after reimmunization; being 50% and 39%, 1 and 2 years after the fourth injection, respectively. Serological surveys suggested a general parallel in the antibody response to vaccine and the level of protection achieved; however, the levels of vibriocidal antibody titres could not be related directly to levels of protection. The overall protection achieved with the 3-year programme of annual reimmunizations was 55% for the group receiving one inoculation annually, and 65% for the group receiving 2 inoculations in the first year followed by annual reimmunizations. When the costs and effectiveness of annual vaccine programmes are compared with those for cholera treatment centres, it becomes clear that the cholera vaccines now available are not appropriate alternatives to treatment in routine cholera control programmes.     

Serological response to cholera revaccination in a semi-closed community in Calcutta

Serological response to cholera revaccination has been studied in a semi-closed community consisting of individuals mostly in the 2-20-years age-group. The subjects had been inoculated against cholera every year at the beginning of the local epidemic season. Pre- and post-vaccination sera were obtained from 29 subjects inoculated with cholera vaccine (test group) and 28 from subjects inoculated with TAB vaccine (control group). These sera were tested for vibriocidal and agglutination titres. The geometrical means of the vibriocidal and agglutination titres of the post-vaccination sera in the test group rose by 490% and 463% respectively. This booster effect was observed mostly in individuals in the 2-14-years age-group, who had low titres (vibriocidal ≤320 and agglutination ≤40) in their prevaccination samples. Revaccination, therefore, appears to be useful as a booster for individuals having low titres.     

Randomized double-blind placebo controlled trial to evaluate the safety and immunogenicity of the live oral cholera vaccine strain CVD 103-HgR in Swiss adults

A randomized, double-blind, placebo controlled trial was conducted in 50 healthy Swiss adults to assess the safety and immunogenicity of the live oral attenuated cholera vaccine candidate strain Vibrio cholerae CVD 103-HgR (classical, Inaba). A single dose of 5 × 10⁸ viable CVD 103-HgR organisms, administered in a buffered liquid formulation, was well tolerated as compared with individuals who received an equivalent amount of heat-killed Escherichia coli K-12 placebo. Eighty-eight percent of subjects receiving CVD 103-HgR mounted a significant (>fourfold) rise in Inaba vibriocidal titre while 68% did so for the heterologous Ogawa serotype. The magnitude of the vibriocidal antibody response (as measured by peak geometric mean titre and by fold-rise in titre over baseline) was greater for the homologous Inaba serotype. Nineteen out of 25 volunteers (76%) responded with a significant (p < 0.05) rise in serum antitoxin levels. No vaccine who received the E. coli K-12 placebo mounted a significant rise in either vibriocidal or antitoxin antibody levels. These results corrobrate the safety and immunogenicity of CVD 103-HgR in healthy adult volunteers.     

Efficacy trial of single-dose live oral cholera vaccine CVD 103-HgR in North Jakarta, Indonesia, a cholera-endemic area

A randomized, double-blind, placebo-controlled efficacy trial of one dose of CVD 103-HgR live oral cholera vaccine was performed in Indonesia from 1993 to 1997. 67,508 persons aged 2-41 years ingested vaccine or placebo and were followed for four years, detecting cholera cases using hospital-based surveillance. A nested reactogenicity study (538 vaccinees, 535 controls) revealed no vaccine-attributable side effects. A nested immunogenicity study (N=657) showed vibriocidal seroresponses in 64-70% of vaccinees vs 1-2% of controls. Cholera incidence was lower than expected. 103 cases of Vibrio cholerae O1 El Tor diarrhea were detected, 93 evaluable for vaccine efficacy (43 vaccine, 50 placebo; efficacy=14%). A suggestion of protection was observed among persons with blood group O [P=0.12]. Only seven cases occurred within six months of vaccination, precluding assessment of short-term efficacy. In Jakarta, single-dose CVD 103-HgR did not confer long-term protection. Short-term protection from a single-dose and long-term protection from two doses have yet to be studied.     

Immunogenicity of two formulations of oral cholera vaccines in Thai volunteers

A formulation of oral vaccine consisting of Vibrio cholerae lipopolysaccharides (LPS), cell-bound haemagglutinin (CHA) and procholeragenoid (P), namely vaccine A, was compared with another formulation, vaccine B, prepared from killed whole vibrios plus procholeragenoid on their immunogenicity and reactogenicity in Thai male volunteers. Volunteers were randomly allocated into three groups. The first two groups received orally three doses of vaccines A and B, respectively at 14-day intervals. Volunteers in group 3 were controls and received orally 100 ml 5% (w/v) NaHCO3 also at 14-day intervals. Serum samples were collected from all volunteers before each immunization. Intestinal lavage was performed 3 to 7 days before the first dose of vaccine or placebo and 7, 21 and 45 days after the last dose. Serum vibriocidal antibodies were determined and class-specific, antigen-specific antibodies of all serum and lavage samples were assessed by indirect enzyme-linked immunosorbent assay (ELISA) using purified LPS, CHA and cholera toxin (CT) as antigens. Diarrhoea occurred in 10 and 40% of the vaccinees ingesting the vaccines A and B, respectively. The immunogenicity of the vaccine B in terms of seroconversion for vibriocidal antibodies and anti-LPS was higher than the vaccine A. Both vaccines had equal immunogenicity concerning serum anti-CT, while the vaccine A was slightly better than the vaccine B on serum anti-CHA response. The immunogenicity of the two vaccines in evoking intestinal responses was different from the systemic one.(ABSTRACT TRUNCATED AT 250 WORDS)     

Report of the 1966-67 cholera vaccine field trial in rural East Pakistan. 3. The lack of effect of prior vaccination or circulating vibriocidal antibody on the severity of clinical cholera

In a controlled study, it has been shown that the prior administration of cholera vaccine had no beneficial effect on the clinical course of cholera as measured by either the condition of the patient on admission to hospital or the subsequent course of the disease. In fact, the disease was, if anything, more severe in those who had received cholera vaccine. Although the presence of a high vibriocidal titre is associated with protection from cholera, pre-existing antibody had no effect on the clinical course of the disease in those patients who developed cholera.     

Augmented immune responses to a booster dose of oral cholera vaccine in Bangladeshi children less than 5 years of age: Revaccination after an interval of over three years of primary vaccination with a single dose of vaccine

We have earlier reported that a single dose of oral cholera vaccine (OCV) is protective in adults and children ≥5 years of age and sustained for 2 years. We enrolled participants (n = 240) from this study, between March-September 2017, over 3 years after receiving a primary single dose. Immune responses were measured in placebo group (Primary Immunization group: PI) and compared with those who received a single dose (Booster Immunization group: BI). The children were 4 to <5 years, 5 to <18 years and adults >18 years. Blood was collected at day 0 (before vaccination) and after receiving 1st and 2nd doses of OCV. Overall, the BI and PI groups showed vibriocidal antibody response after 1st and 2nd dose of vaccination in all age groups to V. cholerae O1 and O139. Young children in the BI group showed significantly higher vibriocidal antibody response two weeks after receiving the first dose as compared to PI group to LPS. Elevated plasma IgA responses to LPS after the first dose were observed among the BI group compared to the PI group among the young children. Mucosal antibody responses measured in fecal extracts showed similar increases as that of vibriocidal and LPS responses in the BI group. These results suggest a single boosting dose of OCV generated immune response in primed population >5 years of age who had earlier received OCV. However, young children who had received OCV earlier, boosting after a single dose, resulted in increased immune responses compared to the PI group. Further studies are needed to assess protection obtained from different strategies, especially for young children and to determine the numbers of primary and booster doses needed. In addition, more information is needed regarding the optimum interval between primary and booster doses to plan future interventions for cholera control.ClinicalTrials.gov Identifier: NCT 02027207.     

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.     

Report of the 1966-67 cholera vaccine field trial in rural East Pakistan. 2. Results of the serological surveys in the study population--the relationship of case rate to antibody titre and an estimate of the inapparent infection rate with Vibrio cholerae

The 1966-67 cholera vaccine field trials in East Pakistan tested 1- and 2-dose schedules of a commercial cholera vaccine in 40 000 children aged 3 months to 14 years. Randomsample serological surveys, made prior to the inoculations and 3 months and 6 months after the inoculations, demonstrated that there was a rise in the vibriocidal titres of the vaccinated children during the first 3 months after inoculation and a subsequent fall by the end of the second 3 months. The antibody response to 2 doses of cholera vaccine was better than the response to a single dose in children under 5 years of age. In children aged 5-14 years, the antibody response was similar for both inoculation schedules. Since the majority of the older children had vibriocidal antibodies before inoculation, the data suggest that the single dose acted as a booster, and this effect was not enhanced by a second inoculation.     

Analysis of efficacy of CVD 103-HgR live oral cholera vaccine against all-cause travellers' diarrhoea in a randomised, double-blind, placebo-controlled study

Enterotoxigenic Escherichia coli (ETEC), which produces heat labile toxin (LT) and/or heat stable toxin (ST), is considered to be the most common known cause of travellers' diarrhoea (TD). Owing to the antigenic similarity between cholera toxin and LT, immunization with inactivated oral B-subunit/whole-cell cholera vaccine (BS-WC) offers short term (3 months) but significant (>67%) protection against TD caused by LT-related ETEC. Since it expresses the cholera toxin B (CTB) subunit, the live attenuated oral cholera vaccine strain CVD 103-HgR, may induce similar protection. A trial was performed to determine if CVD 103-HgR live oral cholera vaccine would provide a protective efficacy of at least 50% against TD. In addition, the protective efficacy of the vaccine against TD specifically due to LT-ETEC and LT/ST-ETEC was determined. Volunteers (n=134) travelling to Indonesia, India, Thailand or West-Africa were randomised to receive either a placebo (n=65) or the vaccine (n=69). In the placebo group, 46% reported an episode of diarrhoea, compared to 52% in the vaccine group. No significant group differences were found with regard to incidence, duration or severity of all caused TD or ETEC-associated TD. However, ETEC-associated TD occurred earlier in the placebo group (median 5 days), compared to the vaccine group (median 15 days). In conclusion, CVD 103-HgR live oral cholera vaccine failed to provide a 50% protection against TD. This study does not exclude that the vaccine may offer a short-lived protection against ETEC-associated TD. However, the power of the study was limited by the unexpected low incidence of LT-ETEC-associated diarrhoea (9% of all TD) compared to ST-associated TD (24% of all TD).     

A single dose of live oral cholera vaccine CVD 103-HgR is safe and immunogenic in HIV-infected and HIV-noninfected adults in Mali.

Despite considerable experience with single-dose, live, oral cholera vaccine CVD 103-HgR in Asia, Europe, and the Americas, the vaccine had not been evaluated in sub-Saharan Africa or on individuals infected with human immunodeficiency virus (HIV). We therefore conducted a randomized, placebo-controlled, double-blind, cross-over clinical trial in 38 HIV-seropositive (without clinical acquired immunodeficiency syndrome (AIDS)) and 387 HIV-seronegative adults in Mali to assess its safety and immunogenicity. Adverse reactions (fever, diarrhoea and vomiting) were observed with similar frequency among vaccine and placebo recipients. The vaccine strain was not isolated from the coprocultures of any subject. The baseline geometric mean titre (GMT) of serum vibriocidal antibody was significantly lower in HIV-seropositives (1:23) than in HIV-seronegatives (1:65) (P = 0.002). Significant rises in vibriocidal antibody were observed in 71% of HIV-seronegatives and 58% of HIV-seropositives, and in 40% of HIV-seropositives with CD4+ counts below 500 per microliter. Following immunization, the peak vibriocidal GMT in HIV-seronegatives was 1:584 versus 1:124 in HIV-seropositives (P = 0.0006); in HIV-seropositives with CD4+ counts < 500 per microliter, the peak vibriocidal GMT was 1:40 (P = 0.03 versus other HIV-seropositives). CVD 103-HgR was safe in HIV-infected Malian adults, although serological responses were significantly attenuated among HIV-seropositives (particularly in those with CD4+ counts < 500 per microliter) relative to HIV-seronegatives. These results encourage further evaluations of this single-dose, oral cholera vaccine in high-risk populations such as refugees in sub-Saharan Africa.     

Field trials of monovalent Ogawa and Inaba cholera vaccines in rural Bangladesh--three years of observation

A controlled cholera vaccine field trial was carried out to test the efficacy of monovalent whole-cell Inaba and Ogawa cholera vaccines and a purified Inaba antigen. This study was designed particularly to study the level of protection produced by these vaccines against homologous and heterologous serotypes and to correlate the results with mouse protection tests and human serological response to the vaccines. A cohort of 45 000 children, aged 0-14 years, was divided into a control group and three vaccine groups. Inoculations were given annually for 2 years just before the start of the cholera season, and follow-up was continued for one additional year. Essentially, all cholera cases were due to the Inaba serotype, so that protection could be studied only against that serotype. Two annual injections of the whole-cell Inaba vaccine gave the highest level of protection, averaging 84% over the 3 years of follow-up; a single injection of the purified Inaba vaccine gave less protection (51%). Two annual injections of the whole-cell Ogawa vaccine failed to protect children under the age of 5 but did produce 48% protection for children aged 5-14 against Inaba cholera. Serological surveys correlated poorly with protection; specifically, the Ogawa vaccine produced high anti-Inaba titres in young children but no protection. The cross-protection against Inaba cholera produced by Ogawa vaccine in the older children is assumed to be due to boosting of naturally acquired immunity in this population. Monovalent vaccine cannot be recommended for general public health use because of the serotype specificity of protection that this study has demonstrated.     

Antibody response in the intestinal secretions of volunteers immunized with various cholera vaccines

The efficacy of various cholera vaccines in eliciting an intestinal antibody response was assessed in human volunteers who received oral live, oral killed, or parenteral cholera vaccines, or placebo. The intestinal immune response in terms of antibacterial and antitoxin antibodies was determined 2 and 4 weeks after immunization. By means of the mouse peritoneum opsonization assay and the infant mouse protection test, antibacterial activity could be detected in the intestinal secretions of volunteers who had been immunized either orally or by the parenteral route. Significant protective activity and duration of immunity were observed with the oral killed vaccine. The bacteriological data indicated the absence of significant intestinal colonization of the live attenuated strain after oral administration, and probably explains the observed lack of effectiveness of the oral vaccine compared with that of the killed vaccine. The predominant immunoglobulin class of intestinal antibody was found to be IgA. None of the vaccines used in the study elicited significant antitoxin activity in the intestinal secretions, as determined by the skin permeability neutralization test.     

A serological survey for cholera antibodies in rural East Pakistan: 1. The distribution of antibody in the control population of a cholera-vaccine field-trial area and the relation of antibody titre to the pattern of endemic cholera*

Controlled cholera vaccine field trials were held in Matlab Bazar in rural East Pakistan in 1963 and 1964. In July—September 1965, a serological survey for cholera antibodies was carried out on a random sample of the field-trial population. Results are given for the control group only, as representative of the pattern found in an endemic cholera area. Only 2% of the blood samples from children under 10 years of age were found to have detectable agglutinating antibody (titres of 1:20 or more), while the proportion in the age-group over 30 years was 27%-30%. Tests for vibriocidal antibody showed that none of the blood samples from children under 1 year of age contained detectable antibody, while 87%-90% of those from adults over 30 years did so. The rise in the geometric mean vibriocidal titre showed an almost linear correlation with a sharp fall in the cholera case rate with age. Since a similar survey in a non-endemic area (Czechoslovakia) did not reveal any rise in antibody titre with age, and since cholera epidemics in areas without recent experience of the disease are characterized by a higher incidence rate in adults than in children, it is suggested that the antibody titres give a measure of the level of immunity in a population.     

A serological survey for cholera antibodies in rural east Pakistan. 2. A comparison of antibody titres in the innunized and control populationd of a cholera-vaccine field-trial area and the relation of antibody titre to cholera case rate

Controlled field trials of a highly antigenic cholera vaccine were held in Matlab Bazar in rural East Pakistan in 1963 and again in 1964. In July—September 1965, a serological survey for cholera antibodies was carried out on a random sample of the field-trial population. This survey revealed that it was possible to demonstrate the effect of a single injection of the cholera vaccine per head on the proportion of the population with detectable vibriocidal and agglutinating antibody 10 and 22 months after injection. More significantly, the reduction in cholera case rate caused by the vaccine could be correlated with the rise in vibriocidal antibody after vaccination, suggesting that the serological response to vaccine in man may be a useful measure of vaccine potency. The survey also indicated that in this endemic cholera area, with a high level of immunity in adults, a single injection of cholera vaccine was in fact a booster dose for the majority of the population. Thus, the results of cholera vaccine field trials in endemic areas cannot be directly extrapolated to predict the effects of the same vaccine in non-endemic areas.     

Scalable production and immunogenicity of a cholera conjugate vaccine

There is a need to develop cholera vaccines that are protective in young children under 5 years of age, which induce long-term immunity, and which can be incorporated into the Expanded Programme of Immunization (EPI) in cholera-endemic countries. The degree of protection afforded by currently available oral cholera vaccines (OCV) to young children is significantly lower than that induced by vaccination of older vaccine recipients. Immune responses that protect against cholera target the O-specific polysaccharide (OSP) of Vibrio cholerae, and young children have poor immunological responses to bacterial polysaccharides, which are T cell independent antigens. To overcome this, we have developed a cholera conjugate vaccine (CCV) containing the OSP of V. cholerae O1, the main cause of endemic and epidemic cholera. Here, we describe production of CCV through a scalable manufacturing process and preclinical evaluation of immunogenicity in the presence and absence of aluminum phosphate (alum) as an adjuvant. The vaccine displays V. cholerae O1 Inaba OSP in sun-burst display via single point attachment of core oligosaccharide to a recombinant tetanus toxoid heavy chain fragment (rTTHc). Two different pilot-scale production batches of non-GMP CCV were manufactured and characterized in terms of physico-chemical properties and immunogenicity. In preclinical testing, the vaccine induced OSP- and lipopolysaccharide (LPS)-specific IgG and IgM responses, vibriocidal responses, memory B cell responses, and protection in a V. cholerae O1 challenge model. The addition of alum to the administered vaccine increased OSP-specific immune responses. These results support evaluation of CCV in humans.     

Pharmacology and toxicology of an oral tablet whole cells inactivated cholera vaccine in Sprague Dawley rats

Here we further investigate the pharmacological and toxicological properties of a cholera vaccine based on inactivated whole cells presented in either enteric coated (COA) or uncoated (U/C) tablet formulation from Vibrio cholerae C7258 strain. Tablets were dispersed in 2 mL drinking water and administered orally to Sprague Dawley rats distributed in five groups (I COA7, II U/C7 immunized at 0, 7, 69 days and III COA14, IV U/C14 immunized at 0, 14, 69 days and V control group). Serum vibriocidal antibody response was measured after the administration of two doses with an interval of 7-14 days. To further investigate the toxicological aspects a third dose was applied 10 weeks after the initial one. Animals were observed daily and water and food consumption was measured every other day. Periodic blood extractions were performed for hematology, biochemistry, and the titer of serum vibriocidal antibodies was determined. Anatomopathological analysis was performed at days 3 or 14 after the third dose. Results from clinical observations, as well as from water and food consumption and body weigh indicated no toxicity of the vaccine product. Meanwhile, no biological differences were found among different groups in hematological, hemo-chemistry, and anatomopathological studies. Moreover, enteric coated and uncoated tablets against human cholera were found to induce an immune response in rats.     

Randomized,double-blind,placebo-controlled trial to evaluate the safety and immunogenicity of live oral cholera vaccine 638 in Cuban adults

A randomized, double-blind, placebo-controlled clinical trial was conducted to evaluate the safety, reactogenicity and the immunogenicity of a 2 × 10⁹ CFU dose of the 638 lyophilized live attenuated cholera vaccine for oral administration, formulated and produced at Finlay Institute, City of Havana, Cuba. Thirty-six healthy female and male adult volunteers from 18 to 40 years old were involved, clinically examined and laboratory tested after the informed consent signature. Adverse events were monitored and seroconversion rates and geometrical mean titer (GMT) of vibriocidal antibodies were tested in volunteer's sera samples. Neither serious adverse events nor other damages to the volunteers due to vaccine or placebo feeding were reported during the clinical follow-up period of this study; none of the adverse events registered within the first 72 h after inoculation were life-threatening for volunteers. Neither severe nor moderate adverse events were reported. Sixty-one percent of subjects showed mild expected adverse events in an interval lower than 24 h up to the first 72 h, 75% of these in the vaccinated group and 18% in the placebo group. Fourteen days after inoculation the GMT of vibriocidal antibodies in the vaccine group significantly increased in comparison to the placebo group. All subjects in the vaccine group (24) seroconverted (100%). Results show that this vaccine is safe, well tolerated and immunogenic in healthy female and male volunteers.