A Study to Evaluate the Efficacy, Safety and Immunogenicity of a Vaccine Designed to Protect Against Infection With Shigella Sonnei in Healthy Adults

Attack rate of shigellosis expressed as percentage of subjects with at least one episode of shigellosis after challenge, and 90% confidence interval (CI) (Clopper-Pearson method). Episodes of shigellosis fulfilling primary case definition: Shedding of S. sonnei 53G accompanied by moderate or severe diarrhea OR shedding with oral temperature greater than or equal to (≥) 38.5°C. Moderate diarrhea consists of 4 to 5 loose or watery (Grade [G]3 to 5) stools or 400 to 800 grams of G3 to 5 stools within 24 hours. Severe diarrhea consists of 6 or more loose or watery (G3 to 5) stools or > 800 grams of G3 to 5 stools within 24 hours or required medical intervention. In case of severe diarrhea, medical intervention is defined as intravenous fluids administration or anticipation of antibiotic treatment before the 5th day after challenge. G3 = viscous opaque liquid or semi-liquid which assumes the shape of the bowl; G4 = watery opaque liquid; G5 = clear watery or mucoid liquid.

Percentage of subjects with shigellosis fulfilling the CHIM expert working group case definition for shigellosis, and 90% confidence interval (CI) (Clopper-Pearson method). According to the working group, the participant must fulfil any of the three following possible endpoints to qualify as having reached the CHIM case definition for this objective: 1. Severe diarrhea defined as [[≥ 6 loose stools in 24 hours] OR [˃800 grams loose stools in 24 hours]; 2. Moderate diarrhea defined as [4-5 loose stools in 24 hours OR 400-800 grams loose stools in 24 hours] AND [oral temperature [≥ 38.0°C OR [≥ 1 moderate constitutional/enteric symptom OR [≥ 2 episodes of vomiting in 24 hours]; 3. Dysentery defined as [[≥ 2 loose stools with gross blood (hemoccult positive) in 24 hours] AND [oral temperature [≥ 38.0°C OR [≥ 1 moderate constitutional/enteric symptom OR [≥ 2 episodes of vomiting in 24 hours].

Percentage of subjects with shigellosis fulfilling the following definition of shigellosis (with 90% confidence interval (CI) - Clopper-Pearson method): 1) severe diarrhea OR 2) moderate diarrhea AND oral temperature ≥ 38.0 °C OR ≥ 1 moderate constitutional/enteric symptom OR 3) dysentery [[≥ 2 loose stools with gross blood (hemoccult positive) in 24 hours] AND [≥ 1 reportable constitutional/enteric symptom]].

Percentage of subjects with more severe shigellosis fulfilling the following definition of more severe shigellosis (with 90% confidence interval (CI) - Clopper-Pearson method): 1) moderate OR severe diarrhea AND oral temperature ≥ 38.0 °C OR ≥ 1 severe constitutional/enteric symptom OR 2) dysentery [[≥ 2 loose stools with gross blood (hemoccult positive) in 24 hours] AND [oral temperature ≥ 38.0°C OR ≥ 1 severe constitutional/enteric symptom]].

Percentage of subjects with 90% CI-Clopper-Pearson method was also measured for: shedding of S.sonnei strain 53G (defined as positivity of ≥1 stool sample by culture/quantitative Polymerase Chain Reaction/both); severe diarrhea; more severe diarrhea; dysentery; confirmed S.sonnei 53G shedding AND moderate or severe diarrhea OR dysentery OR presence of oral temperature ≥ 38.5°C OR presence of 1 or more severe intestinal symptoms (abdominal pain, cramping, nausea, vomiting, gas, and anorexia) abbreviated as "shedding of S.sonnei 53G and […"; disease not fulfilling the protocol primary case definition for shigellosis associated or not with mild to moderate symptoms including: ≥1 stool and no moderate or severe diarrhea evidence, abdominal pain, abdominal cramps, gas, anorexia, nausea, headache, myalgia, malaise, arthralgia, fever, vomiting and intravenous fluid administration. Any=any symptom regardless of intensity grade or relation to study vaccination and/or challenge administration.

The mean number of grade 3-5 stools (and standard deviation) were calculated per subject from challenge to discharge.

Mean and standard deviation (SD) of weights were expressed in grams. The following measures were calculated: mean and SD of the weight of grade 3-5 stools calculated on all subjects (Weight/all subjects), mean and SD of the weight of grade 3-5 stools calculated on subjects with at least one grade 3-5 stool (Weight/subj.with at least 1 grade 3-5 stool), Cumulative mean and SD weight of grade 3-5 stools per subjects, accumulated from challenge to discharge (Cumulative weight/all subjects).

Median time to onset of shigellosis was to be estimated with Kaplan-Meier method among subjects who received the challenge agent. The day associated to the first shigellosis was the time of onset of shigellosis. Subjects who did not have shigellosis were censored at the time on the day of discharge. Median time (in days) to onset of shigellosis and 90% confidence interval (CI) could not be calculated in any of the groups because less than 50% of subjects experienced the event (shigellosis) during the observation period.

Solicited local AEs include: pain, erythema and induration at injection site. Any = occurrence of local adverse event regardless of intensity grade. Any erythema or induration at injection site is any symptom with a surface diameter greater than 25 millimeters.

Solicited systemic AEs include: arthralgia, chills, fatigue, headache, malaise, myalgia, fever (oral temperature ≥ 38.0°C). Any = occurrence of systemic adverse event regardless of intensity and relation to study vaccination.

An unsolicited AE covers any untoward medical occurrence in a clinical investigation subject temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product and reported in addition to those solicited during the clinical study and any solicited symptom with onset outside the specified period of follow-up for solicited symptoms. Any was defined as the occurrence of any unsolicited AE regardless of intensity grade or relation to study vaccination.

An unsolicited AE covers any untoward medical occurrence in a clinical investigation subject temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product and reported in addition to those solicited during the clinical study and any solicited symptom with onset outside the specified period of follow-up for solicited symptoms. Any was defined as the occurrence of any unsolicited AE regardless of intensity grade or relation to study vaccination and/or challenge agent administration.

Serious adverse events (SAEs) assessed include medical occurrences that resulted in death, were life-threatening, required hospitalization or prolongation of hospitalization or resulted in disability/incapacity. Related SAEs = SAEs assessed by the investigator as related to the study vaccination and/or challenge agent administration.

AESI are predefined (serious or non-serious) AEs of scientific and medical concern specific to the product or program, for which ongoing monitoring and rapid communication by the investigator to the sponsor can be appropriate, because such an event might warrant further investigation in order to characterize and understand it.

Among hematological parameters assessed are: Basophils, Eosinophils, Erythrocytes, Hematocrit, Hemoglobin, Leukocytes, Lymphocytes, Monocytes, Neutrophils and Platelets. Below = below the normal laboratory range defined for the specified laboratory parameter; Above = above the normal laboratory range defined for the specified laboratory parameter; Within = within the normal laboratory range defined for the specified laboratory parameter. Category naming has been defined as follows: Parameter, time point, range indicator at Baseline, range indicator at the specified time point: e.g.: "Basophils, Day 8, Within, Within ". Note: All subjects whose neutrophil value was below the threshold defined in the Protocol, at any time during the study, were re-tested until neutropenia resolution.

Anti-S. sonnei LPS IgG antibody concentrations are presented as geometric mean concentrations (GMCs), determined by Enzyme-linked immunosorbent assay (ELISA) and expressed in ELISA units per milliliter (EU/mL). Note: regarding the "28 days after second vaccination" protocol timing, sample collection could have been performed either at Day 56 or at Day 57. For all the subjects, samples were collected at Day 56, and therefore, results are presented for "Day 56 (27 days after the second vaccination)" timing.

Anti-S. sonnei LPS IgG antibody concentrations are presented as GMCs, as determined by ELISA and expressed in EU/mL. Note: regarding the "28 days after second vaccination" protocol timing, sample collection could have been performed either at Day 56 or at Day 57. For all the subjects, samples were collected at Day 56, and therefore, results are presented for "Day 56 (27 days after the second vaccination)" timing.

This antibody response cut-off was based on the results of the previous Phase I studies and estimated results of the median antibody titer after natural infection by S. sonnei. The threshold 121 EU/mL planned per protocol has been recalibrated to 268 EU/mL following an investigation of reliability of the ELISA assay. Note: regarding the "28 days after second vaccination" protocol timing, sample collection could have been performed either at Day 56 or at Day 57. For all the subjects, samples were collected at Day 56, and therefore, results are presented for "Day 56 (27 days after the second vaccination)" timing.

Seroresponse definition as reported in the protocol was assay specific and specifically related to assay, as run in Marburg Lab for the previous GVGH Shigella studies. This assay was further characterized and optimized before being used in GVGH for the current Phase 2b study. Since the assay used in current study is not comparable with the assay used in previous GVGH studies, the seroresponse definition is no longer appropriate (as it is valid only for Marburg assay). With the acknowledgment that seroresponse results are no longer meaningful, the study team choose to report the results for transparency. Note: regarding the "28 days after second vaccination" protocol timing, sample collection could have been performed either at Day 56 or at Day 57. For all the subjects, samples were collected at Day 56, and therefore, results are presented for "Day 56 (27 days after the second vaccination" timing.