In a field trial conducted in Bangladesh, ingestion of either B subunit-killed whole cell (BS-WC) or killed whole cell (WC) oral cholera vaccines by mothers was associated with a 47% reduction of the risk of cholera in their non-vaccinated children aged under 36 months. Because vaccine-induced breast-milk immunity seemed a possible explanation for these findings, we evaluated anti-lipopolysaccharide (LPS) and anti-cholera toxin (CT) IgA antibody responses in breast milk collected during the trial from 53 lactating women who ingested three doses of BS-WC, WC, or an Escherichia coli K12 strain (K12). Despite induction of moderate vibriocidal (1.4 to 2.0-fold) and anti-CT (4.5-fold) serum antibody responses, the vaccines did not elicit significant rises of anti-LPS or anti-CT IgA breast-milk antibodies. The failure of the vaccines to elicit significant levels of breast-milk anti-cholera antibodies suggests an alternative explanation for protection of young children by maternal vaccination, such as interruption of maternal-child transmission of Vibrio cholerae 01.

The seventh cholera pandemic, caused by Vibrio cholerae O1 biotype El Tor, began in Celebes (Sulawesi), Indonesia, in 1961, reached Africa by 1970 (1, 2) and persisted thereafter, causing both endemic and epidemic disease (3-5). One of the most dramatic epidemiological events in this pandemic was the explosive outbreak of cholera that swept through Rwandan refugee camps near Goma, Zaire, during several weeks in 1994, when an estimated 70000 cases and 12000 deaths occurred (6). Several months after this tragedy, public health experts convened at WHO to consider the possible role that the new generation of oral cholera vaccines (7) might play in helping to control cholera in refugee camps and other emergency situations. It is unlikely that any vaccine could have had a marked impact on the outbreak in Goma because of the unusual circumstances in that specific setting (8). Nevertheless, it is reasonable to expect that the new vaccines may prove beneficial in future refugee situations where cholera poses a public health threat (9-11). In less acute contexts, vaccinating against cholera could serve a useful adjunct role, particularly with an easily administered oral vaccine that rapidly confers protection after a single dose.

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.

Enterotoxigenic Escherichia coli (ETEC) is one of the leading causes of diarrhea among Israeli soldiers serving in field units. Two double-blind placebo-controlled, randomized trials were performed among 155 healthy volunteers to evaluate the safety and immunogenicity of different lots of the oral, killed ETEC vaccine consisting of two doses of whole cells plus recombinantly produced cholera toxin B subunit (rCTB). The two doses of vaccine lot E005 and the first dose of vaccine lot E003 were well tolerated by the volunteers. However, 5 (17%) vaccinees reported an episode of vomiting a few hours after the second dose of lot E003; none of the placebo recipients reported similar symptoms. Both lots of vaccine stimulated a rate of significant antibody-secreting cell (ASC) response to CTB and to colonization factor antigen I (CFA/I) after one or two doses, ranging from 85 to 100% and from 81 to 100%, respectively. The rate of ASC response to CS2, CS4, and CS5 was slightly lower than the rate of ASC response induced to CTB, CFA/I, and CS1. The second vaccine dose enhanced the response to CTB but did not increase the frequencies or magnitude of ASC responses to the other antigens. The two lots of the ETEC vaccine induced similar rates of serum antibody responses to CTB and CFA/I which were less frequent than the ASC responses to the same antigens. Based on these safety and immunogenicity data, an efficacy study of the ETEC vaccine is under way in the Israel Defense Force.

A controlled cholera vaccine field trial was carried out in rural East Pakistan during the 1966-67 cholera season. A commercial cholera vaccine of average potency was tested in 40 000 children aged 3 months to 14 years in 1- and 2-dose schedules. In the cholera season extending for 8 months following immunization, a single dose produced an over-all protection of 46%; 2 doses at an interval of 1 month provided 64% protection. The single dose was virtually ineffective in children under 5 years, but provided significant protection in older children. The enhanced effect of the 2-dose schedule was primarily due to the boosting of protection in children under the age of 5 years. The duration of significant protection, even with the 2-dose schedule, did not appear to extend beyond the first 3 months of the 8-month cholera season.

Peru-15 is a live attenuated oral vaccine derived from a Vibrio cholerae O1 El Tor Inaba strain by a series of deletions and modifications, including deletion of the entire CT genetic element. Peru-15 is also a stable, motility-defective strain and is unable to recombine with homologous DNA. We wished to determine whether a single oral dose of Peru-15 was safe and immunogenic and whether it would provide significant protection against moderate and severe diarrhea in a randomized, double-blind, placebo-controlled human volunteer cholera challenge model. A total of 59 volunteers were randomly allocated to groups to receive either 2 × 108 CFU of reconstituted, lyophilized Peru-15 vaccine diluted in CeraVacx buffer or placebo (CeraVacx buffer alone). Approximately 3 months after vaccination, 36 of these volunteers were challenged with approximately 105 CFU of virulent V. cholerae O1 El Tor Inaba strain N16961, prepared from a standardized frozen inoculum. Among vaccinees, 98% showed at least a fourfold increase in vibriocidal antibody titers. After challenge, 5 (42%) of the 12 placebo recipients and none (0%) of the 24 vaccinees had moderate or severe diarrhea (≥3,000 g of diarrheal stool) (P = 0.002; protective efficacy, 100%; lower one-sided 95% confidence limit, 75%). A total of 7 (58%) of the 12 placebo recipients and 1 (4%) of the 24 vaccinees had any diarrhea (P < 0.001; protective efficacy, 93%; lower one-sided 95% confidence limit, 62%). The total number of diarrheal stools, weight of diarrheal stools, incidence of fever, and peak stool V. cholerae excretion among vaccinees were all significantly lower than in placebo recipients. Peru-15 is a well-tolerated and immunogenic oral cholera vaccine that affords protective efficacy against life-threatening cholera diarrhea in a human volunteer challenge model. This vaccine may therefore be a safe and effective tool to prevent cholera in travelers and is a strong candidate for further evaluation to prevent cholera in an area where cholera is endemic.

<b>

BACKGROUND:

</b>The effects of oral rehydration solution (ORS) with reduced osmolarity on children with acute watery diarrhoea are known, but little is known about the effects of such ORS on adults with cholera. We aimed to compare the efficacy and safety of an ORS with reduced osmolarity with that of standard WHO ORS in adults with cholera.<b>

METHODS:

</b>We undertook a double-blind, controlled clinical trial in adults with severe cholera at the International Centre for Diarrhoeal Disease Research, Bangladesh. Our primary outcomes were mean stool output in the 24 h after randomisation, proportion of patients who needed unscheduled intravenous therapy, and proportion of patients with biochemical hyponatraemia 24 h after randomisation.<b>

FINDINGS:

</b>147 patients received ORS with reduced osmolarity and 153 received standard WHO ORS. There was no significant difference between the two groups in terms of main outcome variables: mean initial 24 h and total stool output (reduced osmolarity vs standard WHO ORS 212 [SE 8] vs 207 [8] and 284 [13] vs 273 [13] g/kg respectively), duration of diarrhoea (46 [1.5] vs 43 [1.5]). The proportion of patients vomiting during the first 24 h and the proportion who received unscheduled intravenous infusion during the first 24 h was similar between groups. More patients on reduced osmolarity ORS than on standard WHO ORS developed hyponatraemia during the first 24 h, defined as serum sodium concentration below 130 mmol/L (29 of 142 vs 16 of 150; odds ratio 2.1 [95% CI 1.1-4.1]). However, all hyponatraemic patients in both groups were symptom-free and the proportion of patients with serum sodium concentration below 125 mmol/L was similar between groups.<b>

INTERPRETATION:

</b>There was no difference in clinical outcome between cholera patients treated with reduced osmolarity ORS solution and those treated with standard WHO ORS. The risk of increased incidence of symptom-free hyponatraemia in patients with cholera treated with an ORS with reduced osmolarity should be further assessed by meta-analysis. The risk should be taken into account when choice of ORS is made in areas in which cholera is endemic.

Two randomized, double-blinded trials assessed the safety and immunogenicity of an oral, killed enterotoxigenic Escherichia coli (ETEC) plus cholera toxin B subunit vaccine in Egyptian children. Two doses of vaccine or E. coli K-12 were given 2 weeks apart to 105 6- to 12-year-olds and 97 2- to 5-year-olds. Safety was monitored for 3 days after each dose. Blood was collected before immunization and 7 days after each dose to measure immune responses. Few children reported postdosing symptoms, with no differences in the frequency of symptoms between treatment groups. Most vaccinees had an IgA antibody-secreting cell response against colonization factor antigen I (100%, 6-12 years; 95%, 2-5 years), coli surface antigen 2 (92%, 6-12 years; 83%, 2-5 years), and coli surface antigen 4 (93%, 6-12 years). Vaccination evoked a >/=4-fold rise in antitoxic IgA and IgG titers in 93% and 81% of children, respectively. In conclusion, the oral ETEC vaccine was safe and immunogenic in 2- to 12-year-old children, justifying further evaluation in infants.

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.

A phase II safety and immunogenicity study of an oral-formalin inactivated enterotoxigenic Escherichia coli (ETEC) vaccine containing six colonization factors (CFA/I, CS1, CS2, CS3, CS4, CS5) and 1mg of recombinant cholera toxin B subunit (the CF-BS-ETEC vaccine) was carried out in an urban slum of Dhaka city in Bangladesh. The study was carried out in a double blinded, placebo controlled design in 158 children, 18-36 months of age. Children were given two doses of the CF-BS-ETEC vaccine or the placebo which consisted of E. coli K12. The vaccine was well tolerated. The immune response was studied in 60 children (30 each in the placebo and vaccine group). Significant vaccine specific IgA antibody-secreting cell (ASC) responses were seen 7 days after ingestion of the first and second dose of the vaccine. The responses to CFA/I (P<or=0.001), CS2 (P=0.021), CS4 (P=0.009) and rCTB (P<or=0.001) were elevated in the vaccines in comparison to the pre-immune values and in comparison to those seen in the placebo recipients (P=0.018 to <0.001). Vaccines but not placebo recipients also showed significantly increased IgM ASC responses to all three CF antigens that were tested (P=0.012 to <0.001) and IgG-ASCs to rCTB (P<0.001). Peak ASC levels were reached after one dose of the vaccine with no further increase or decrease after the second dose. The vaccine recipients also responded with IgA plasma antibodies to CFA/I, CS1, CS2, CS4 and rCTB after one or two doses of the vaccine (P=0.01 to <0.001). Subjects in the placebo group failed to mount responses to any of the antigens. The vaccine also induced responses in mucosal IgA antibodies in feces to CFA/I, CS2 and rCTB (61, 88 and 69% responder frequency, respectively) and the magnitude of the response was elevated in comparison to the pre-immune levels (P=0.031 to <0.001) and to the levels of the control group (P=0.003 to <0.001). This study thus shows that the CF-BS-ETEC vaccine is well tolerated in children, 18-36 months of age and gives rise to significant systemic and mucosal IgA antibody responses.