Oral, inactivated, whole cell enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine: results of the initial evaluation in children. PRIDE Study Group. Induction of systemic antifimbria and antitoxin antibody responses in Egyptian children and adults by an oral, killed enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine. Safety and immunogenicity of an oral, killed enterotoxigenic Escherichia coli-cholera toxin B subunit vaccine in Egyptian adults. Introductory evaluation of an oral, killed whole cell enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine in Egyptian infants. Transcutaneous immunization with the heat-labile toxin (LT) of enterotoxigenic Escherichia coli (ETEC): protective efficacy in a double-blind, placebo-controlled challenge study. A double-blind, placebo-controlled trial to evaluate the efficacy of PTL-003, an attenuated enterotoxigenic E. coli (ETEC) vaccine strain, in protecting against challenge with virulent ETEC. Double-blind, randomized, placebo controlled pilot study evaluating efficacy and reactogenicity of an oral ETEC B-subunit-inactivated whole cell vaccine against travelers' diarrhea (preliminary report). Analysis of efficacy of CVD 103-HgR live oral cholera vaccine against all-cause travellers' diarrhoea in a randomised, double-blind, placebo-controlled study. Reduced doses of oral killed enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine is safe and immunogenic in Bangladeshi infants 6-17 months of age: dosing studies in different age groups. Safety and immunogenicity of an oral inactivated enterotoxigenic Escherichia coli vaccine. Safety and immunogenicity of two different lots of the oral, killed enterotoxigenic escherichia coli-cholera toxin B subunit vaccine in Israeli young adults. Randomised, double-blind, safety and efficacy of a killed oral vaccine for enterotoxigenic E. Coli diarrhoea of travellers to Guatemala and Mexico. Cross-protection by B subunit-whole cell cholera vaccine against diarrhea associated with heat-labile toxin-producing enterotoxigenic Escherichia coli: results of a large-scale field trial. Use of a patch containing heat-labile toxin from Escherichia coli against travellers' diarrhoea: a phase II, randomised, double-blind, placebo-controlled field trial. Safety, Immunogenicity, and Protective Efficacy of the Whole-Cell/Recombinant B Subunit (WC/rBS) Oral Cholera Vaccine Against Travelers' Diarrhea. Safety and immunogenicity of an oral, inactivated enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine in Bangladeshi children 18-36 months of age. Prevention of travellers' diarrhoea by oral B-subunit/whole-cell cholera vaccine. Lack of prophylactic efficacy of an enteric-coated bovine hyperimmune milk product against enterotoxigenic Escherichia coli challenge administered during a standard meal. Dose-dependent circulating immunoglobulin A antibody-secreting cell and serum antibody responses in Swedish volunteers to an oral inactivated enterotoxigenic Escherichia coli vaccine. Milk immunoglobulin with specific activity against purified colonization factor antigens can protect against oral challenge with enterotoxigenic Escherichia coli.
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. We assessed serologic responses to an oral, killed whole-cell enterotoxigenic Escherichia coli plus cholera toxin B-subunit (ETEC-rCTB) vaccine in 73 Egyptian adults, 105 schoolchildren, and 93 preschool children. Each subject received two doses of vaccine or placebo 2 weeks apart, giving blood before immunization and 7 days after each dose. Plasma antibodies to rCTB and four vaccine-shared colonization factors (CFs) were measured by enzyme-linked immunosorbent assay. Immunoglobulin A (IgA) antibodies to rCTB and CFA/I were measured in all subjects, and those against CS1, CS2, and CS4 were measured in all children plus a subset of 33 adults. IgG antibodies to these five antigens were measured in a subset of 30 to 33 subjects in each cohort. Seroconversion was defined as a >2-fold increase in titer after vaccination. IgA and IgG seroconversion to rCTB was observed in 94 to 95% of adult vaccinees, with titer increases as robust as those previously reported for these two pediatric cohorts. The proportion showing IgA seroconversion to each CF antigen among vaccinated children (range, 70 to 96%) and adults (31 to 69%), as well as IgG seroconversion in children (44 to 75%) and adults (25 to 81%), was significantly higher than the corresponding proportion in placebo recipients, except for IgA responses to CS2 in adults. IgA anti-CF titers peaked after one dose in children, whereas in all age groups IgG antibodies rose incrementally after each dose. Independently, both preimmunization IgA titer and age were inversely related to the magnitude of IgA responses. In conclusion, serologic responses to the ETEC-rCTB vaccine may serve as practical immune outcome measures in future pediatric trials in areas where ETEC is endemic. Enterotoxigenic Escherichia coli (ETEC) is the leading cause of bacterial diarrhea in young children in developing countries. The safety and immunogenicity of a killed, oral ETEC vaccine consisting of whole cells plus recombinantly produced cholera toxin B subunit (rCTB) was evaluated in Egypt, which is endemic for ETEC diarrhea. Seventy-four healthy Egyptian adults (21-45 years old) were randomized and received two doses of the ETEC/rCTB vaccine (E003) or placebo 2 weeks apart. The frequency of adverse events after either dose did not differ by treatment group, and no severe adverse events were reported. After vaccination, peripheral blood IgA B cell responses to CTB (100%) and to vaccine colonization factor antigens CFA/I (94%), CS4 (100%), CS2 (81%), and CS1 (69%) were significantly higher than response rates for the placebo group. These favorable results in Egyptian adults indicate that the ETEC/rCTB vaccine is a promising candidate for evaluation in younger age groups in this setting. We conducted the first trial to assess the safety and immunogenicity of an oral, killed enterotoxigenic Escherichia coli plus cholera toxin B-subunit vaccine in children <2 years old.
                Three doses of vaccine or killed E. coli K-12 control were given at 2-week intervals to 64 Egyptian infants, 6 to 18 months old, in a randomized, double blind manner. Adverse events were monitored for 3 days after each dose. Blood was collected before immunization and 7 to 10 days after each dose to assess vaccine-specific serologic responses.
                There was no statistically significant intergroup difference in the percentage of subjects reporting the primary safety endpoint (diarrhea or vomiting) after the first (31%, vaccine; 30%, control) or third (14%, vaccine; 18%, control) dose, whereas there was a trend toward greater reporting in the vaccine group after Dose 2 (36%, vaccine; 18%, control; P = 0.052). The percentage of children showing IgA seroconversion after any dose was higher in the vaccine than the control group for recombinant cholera toxin B-subunit (97% vs. 46%), colonization factor antigen I (61% vs. 18%) and coli surface antigen 4 (39% vs. 4%) (P < 0.001 for each comparison). IgG seroconversion rates in the vaccine and control groups were 97 and 21% to recombinant cholera toxin B-subunit (P < 0.001), 64 and 29% for colonization factor antigen I (P < 0.01), 53 and 21% for coli surface antigen 2 (P < 0.05) and 58 and 4% for coli surface antigen 4 (P < 0.001), respectively. The third vaccine dose was followed by augmented IgG antitoxin titers.
                The oral enterotoxigenic E. coli vaccine was safe and immunogenic in this setting in Egyptian infants. An enterotoxigenic Escherichia coli (ETEC) vaccine could reduce diarrhea among children in developing countries and travelers to these countries. The heat-labile toxin (LT) of ETEC is immunogenic but too toxic for oral or nasal vaccines.
                In a double-blind, placebo-controlled trial, 59 adults were randomized to receive 50 microg of LT or placebo in a patch applied to alternating arms on days 0, 21, and 42. On day 56, 27 vaccinees and 20 controls were challenged orally with 6x10(8) cfu of LT+/ST+ ETEC.
                100 and 97% of vaccinees had 4-fold increases in anti-LT IgG and IgA, and 100 and 90% developed IgG- and IgA-antibody-secreting cell responses. The study did not meet the primary endpoint: 82% of vaccinees and 75% of controls had moderate to severe ETEC illness. However, vaccinees with ETEC illness had lower numbers (6.8 versus 9.7, p=0.04) and weights of loose stools (840 g versus 1147 g, p<0.05), a decreased need for intravenous fluids (14% versus 40%, p=0.03) and a delayed onset of diarrhea (30 h versus 22 h, p=0.01).
                Transcutaneous LT vaccination induced anti-toxin immune responses that did not prevent but mitigated illness following a high-dose challenge with a virulent LT+/ST+ ETEC strain. Enterotoxigenic E. coli (ETEC) are an important cause of diarrhea in developing countries, especially among indigenous children and travelers. In this randomized, double-blind, placebo-controlled trial, a live, attenuated CS1/CS3 ETEC strain, PTL-003, was tested as a potential vaccine strain. Thirty-three subjects drank buffered solutions containing either PTL-003 or placebo on Days 0 and 10 and were challenged with virulent CS1/CS3 ETEC strain E24377A on Day 28. The vaccine did not protect against moderate to severe ETEC illness (the primary endpoint), but it did prime subjects for a rapid antibody response to CS1 and CS3 after challenge, suggesting that a dose of vaccine on Day 28 might improve the immune response to the vaccine. Higher serum anti-CS3 IgA titers at the time of challenge correlated with less severe diarrheal illness. Diarrhea caused by enterotoxigenic E.coli (ETEC) is an important health problem in developing countries and in travelers to these areas. In previous trials formulations of ETEC vaccines containing the B-subunit of cholera toxin, which is antigenically similar to the heat labile enterotoxin of ETEC, and the most prevalent colonization factor antigens of ETEC, were shown to stimulate relevant mucosal immune responses in volunteers from Sweden and Egypt. 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). The oral-formalin inactivated whole cell enterotoxigenic Escherichia coli (ETEC) vaccine needs to be further tested in developing countries in order to determine the dose at which it will be safe and immunogenic for infants who are the target population for the vaccine. To determine the immunogenicity of reduced doses, studies were first carried out in children, 2-12 years of age (n = 60). The full, half or a quarter doses of the vaccine were comparable in immunogenicity with similar frequency of responses seen to the different antigens (P = NS). Following this result, a pilot study carried out in infants, 6-17 months of age (n = 50), showed that the frequency of episodes of vomiting was lowest when a quarter of the full dose was used. The infants however showed comparable immune responses to the half and quarter dose of vaccine that was tested (P = NS). Based on these results in the infants, a randomized double blind placebo-controlled Phase II study was carried out in 158 children, 6-17 months of age, where a quarter dose of the ETEC vaccine was tested. Adverse events of mild vomiting were seen in only 4% of vaccinees and in 2.5% of placebo recipients. The IgA-antibody secreting cell (ASC) responses to CFA/I (GM: 28.1 ASC/10(7) PBMC) and BS (GM: 55.7 ASC/10(7) PBMC) were elevated compared to placebo recipients (CFA/I-2.0; BS-4.8 ASC/10(7) PBMC) (P = 0.01 to < 0.001). The plasma-IgA antibody titers in vaccinees were also significantly elevated to CFA/I (GM-93.00), CS1 (GM-62.0), CS2 (GM-55.0), CS4 (GM-66.0) and BS (1057.0) compared to preimmune levels or responses or levels in placebo recipients (P < or = 0.05-0.001). This study thus demonstrates that reduced doses of the ETEC vaccine is immunogenic in children and infants as well as safe in infants down to 6 months of age. The safety and immunogenicity of two different lots, 001 and 003, of an oral inactivated enterotoxigenic Escherichia coli (ETEC) vaccine consisting of a mixture of formalin-killed whole bacteria expressing the most prevalent colonisation factor antigens, i.e. CFA/I, CFA/II and CFA/IV and recombinantly produced cholera B subunit (rCTB) have been evaluated in Swedish volunteers. Neither of the two vaccine preparations, containing different CFA/II-expressing strains but otherwise identical, gave rise to any significant side-effects. Mucosal immune responses, as reflected in antibody-secreting cell (ASC) responses in peripheral blood, were studied after two doses of vaccine and did not differ significantly for the two vaccine lots. Vaccination induced high levels of CTB-specific IgA ASCs in 100% of the volunteers, and significant IgA ASC responses (9- to 36-fold) were noted in 84% of them against CFA/I, in 87% against CFA/II subcomponents CS1-CS3 and in 91% against CFA/IV subfactors CS4 and/or CS5. The frequencies and magnitudes of CFA IgA ASC responses were similar when giving the vaccine with a 1 or 2 week interval. Results from serological analyses showed that the local IgA responses against CFAs are only infrequently associated with serum antibody titre rises. 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. We tested the efficacy of a killed oral vaccine for enterotoxigenic Escherichia coli (ETEC) diarrhoea to determine if two doses of vaccine with colonization factor antigens (CF) and cholera B subunit would protect against ETEC diarrhoea of travellers. Six hundred seventy-two healthy travellers going to Mexico or Guatemala were studied in a prospective, randomised, placebo-controlled trial. The primary outcome was a vaccine preventable outcome (VPO), defined as an episode of ETEC diarrhoea with an ETEC organism producing heat labile toxin (LT) or CF homologous with the vaccine, without other known causes. The vaccine was safe and stimulated anti-heat labile toxin antibodies. There was a significant decrease in more severe VPO episodes (PE=77%, p=0.039) as defined by symptoms that interfered with daily activities or more than five loose stools in a day, although the total number of VPO events did not differ significantly in the vaccine and placebo groups. We conclude that the new oral ETEC vaccine reduces the rate of more severe episodes of traveller's diarrhoea (TD) due to VPO-ETEC, but it did not reduce the overall rate of ETEC diarrhoea or of travellers' diarrhoea due to other causes. The B subunit (BS) of cholera toxin and that of the heat-labile enterotoxin (LT) of enterotoxigenic Escherichia coli (ETEC) are antigenically similar. We therefore assessed whether a combined cholera toxin BS/whole-cell (BS-WC) oral vaccine against cholera conferred cross-protection against LT-producing ETEC (LT-ETEC) diarrhea in a randomized, double-blind field trial among rural Bangladeshi children and women. The 24,770 persons who ingested two or more doses of BS-WC vaccine were compared with 24,842 controls who took two or more doses of killed whole-cell (WC) oral cholera vaccine. Sixty-seven percent fewer episodes of LT-ETEC diarrhea were noted in the BS-WC group than in the WC group during short-term (three-month) follow-up (P less than .01), but no reduction was evident during the ensuing nine months. Short-term protection was particularly notable against LT-ETEC diarrhea causing life-threatening dehydration (protective efficacy, 86%; P less than .05). Enterotoxigenic Escherichia coli (ETEC) is a major cause of travellers' diarrhoea. We investigated the rate of diarrhoea attacks, safety, and feasibility of a vaccine containing heat-labile enterotoxin (LT) from ETEC delivered to the skin by patch in travellers to Mexico and Guatemala.
                In this phase II study, healthy adults (aged 18-64 years) who planned to travel to Mexico or Guatemala and had access to a US regional vaccination centre were eligible. A centralised randomisation code was used for allocation, which was masked to participants and site staff. Primary endpoints were to investigate the field rate of ETEC diarrhoea, and to assess the safety of heat-labile toxins from E coli (LT) delivered via patch. Secondary endpoints included vaccine efficacy against travellers' diarrhoea and ETEC. Participants were vaccinated before travel, with two patches given 2-3 weeks apart. Patches contained either 37.5 mug of LT or placebo. Participants tracked stool output on diary cards in country and provided samples for pathogen identification if diarrhoea occurred. Diarrhoea was graded by the number of loose stools in 24 h: mild (three), moderate (four or five), and severe (at least six). Analysis was per protocol. The trial is registered with ClinicalTrials.gov, number NCT00516659.
                Recruitment closed after 201 participants were assigned patches. 178 individuals received two vaccinations and travelled and 170 were analysed. 24 (22%) of 111 placebo recipients had diarrhoea, of whom 11 (10%) had ETEC diarrhoea. The vaccine was safe and immunogenic. The 59 LT-patch recipients were protected against moderate-to-severe diarrhoea (protective efficacy [PE] 75%, p=0.0070) and severe diarrhoea (PE 84%, p=0.0332). LT-patch recipients who became ill had shorter episodes of diarrhoea (0.5 days vs 2.1 days, p=0.0006) with fewer loose stools (3.7 vs 10.5, p<0.0001) than placebo.
                Travellers' diarrhoea is a common ailment, with ETEC diarrhoea illness occurring in 10% of cases. The vaccine patch is safe and feasible, with benefits to the rate and severity of travellers' diarrhoea. Background: A prospective, randomized, double-blind, placebo-controlled trial of WC/rBS oral cholera vaccine was conducted in 502 U.S. college students attending summer educational programs in Mexico. Methods: Two doses of vaccine (or placebo) were administered 10 days apart immediately after arrival in Mexico. Results: The vaccine was free of significant adverse side effects. Anticholera toxin seroconversion was demonstrated in 86.7% of vaccinees compared to 8.2% of controls (p <.001). Postvaccination titers varied according to disease status (travelers' diarrhea) and enteropathogen isolated when disease developed. Protective efficacy (PE) against enterotoxigenic Escherichia coli (ETEC) diarrhea was 50% (95% CI, 14-71%), beginning 7 days after the second dose of WC/rBS. However, 74% of ETEC cases occurred within 7 days of the second dose, when no efficacy was demonstrated. Conclusions: Vaccines employed to prevent travelers' diarrhea will likely need to be administered before arrival in a developing country to be predictably beneficial. An unexpected finding was that infection with LT-ETEC after primary oral cholera immunization appears to augment the antitoxin response to WC/rBS vaccine. (J Travel Med 2:22-27, 1995) 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. B-subunit/whole-cell cholera vaccine (BS-WC) has been shown to give Bangladeshi mothers and children only 3 months' protection against severe diarrhoea due to enterotoxigenic Escherichia coli (ETEC). Since a long-lasting effect is not necessary for protection against travellers' diarrhoea, a prospective double-blind study was conducted among tourists who went to Morocco from Finland. 307 tourists received two oral doses of BS-WC, whereas 308 controls received a placebo before departure. A research team went out with tourists and a laboratory for enteric pathogens was set up on location. A faecal specimen was taken from 100 randomly selected subjects before departure, from all travellers with diarrhoea, and routinely after return. Enteropathogenic bacteria were not isolated from any of the pre-departure specimens but were present during or after the holiday in 47% of tourists with travellers' diarrhoea, and in 14% of those without diarrhoea. BS-WC induced a 52% protection (p = 0.013) against diarrhoea caused by ETEC. The protection was better for mixed infections (65%, p = 0.016). The protective efficacy against a combination of ETEC and any other pathogen was 71% (p = 0.02), and that against ETEC plus Salmonella enterica even better at 82% (p = 0.01). Partial protection against travellers' diarrhoea is thus obtainable by active immunisation with BS-WC. Orally administered bovine immunoglobulins with specific activity against colonization factors of enterotoxigenic Escherichia coli (ETEC) could provide passive protection against ETEC challenge in volunteers. Twenty healthy adult volunteers ingested either a placebo or a partially enteric-coated preparation of bovine immunoglobulins with activity against the colonization factor antigens CFA/I, CS3, and CS6 and then were challenged with ETEC strain E24377A (CS1+, CS3+) administered with a standard meal. There was no difference in the incidence or severity of diarrhea among the 10 volunteers who received the bovine immunoglobulins and the 10 who received placebo. Either the specificity or titer of anti-colonization factor antibodies or the formulation of antibodies in this product was not adequate to provide passive protection against ETEC challenge. The immunogenicity of different preparations of an oral inactivated enterotoxigenic Escherichia coli (ETEC) vaccine was evaluated in Swedish volunteers previously unexposed to ETEC infection. The vaccine preparations consisted of recombinant cholera toxin B subunit (CTB) and various amounts of formalin-killed whole bacteria expressing the most prevalent colonization factor antigens (CFAs). Significant immunoglobulin A (IgA) antibody-secreting cell (ASC) responses against CTB and the various CFA components were seen in a majority of volunteers after two doses of ETEC vaccine independent of the vaccine lot given. The IgA ASC responses against CTB were significantly higher after the second than after the first immunization, whereas the CFA-specific IgA ASC responses were almost comparable after the first and second doses of ETEC vaccine. Two immunizations with one-third of a full dose of CFA-ETEC bacteria induced lower frequencies of IgA ASC responses against all the different CFAs than two full vaccine doses, i.e., 63 versus 80% for CFA/I, 56 versus 70% for CS1, 31 versus 65% for CS2, and 56 versus 75% for CS4. The proportion of vaccinees responding with rises in the titer of serum IgA antibody against the various CFA antigens was also lower after immunization with the reduced dose of CFA-ETEC bacteria. These findings suggest that measurements of circulating IgA ASCs can be used not only for qualitative but also for quantitative assessments of the immunogenicity of individual fimbrial antigens in various preparations of ETEC vaccine. Enterotoxigenic Escherichia coli (ETEC) is the most commonly isolated pathogen responsible for travelers' diarrhea and the cause of up to 650 million cases of pediatric diarrhea per year in the developing world. As a safe alternative to the prophylactic use of antibiotics, a hyperimmune bovine milk antibody product with specific activity against purified colonization factor antigens (CFAs) was developed and evaluated in a human challenge study. Twenty-five healthy adult volunteers were challenged orally with 10(9) cfu of a virulent CFA/I-bearing ETEC. In the randomized double-blind trial, 7 of 10 volunteers receiving a lactose-free placebo developed clinical diarrhea after challenge, compared with only 1 of 15 cases in volunteers receiving active product (Fisher's exact test, P < .0017). It is concluded that antibodies against CFAs alone are sufficient for protection and that prophylaxis with milk-derived immunoglobulin is a feasible alternative to existing drug interventions.
There is currently insufficient evidence from RCTs to support the use of the oral cholera vaccine Dukoral® for protecting travellers against ETEC diarrhoea. Further research is needed to develop safe and effective vaccines to provide both short and long-term protection against ETEC diarrhoea.