The aim of the current clinical study is to evaluate, for the first time in humans (FTIH), the safety and immunogenicity of the altSonflex1-2-3 candidate vaccine against S. sonnei and S. flexneri serotypes 1b, 2a, and 3a. The vaccine will be first administered in adults 18 to 50 years of age in Europe. Subsequently, the vaccine will be administered to a shigellosis-endemic population in Africa, first in adults 18 to 50 years of age, then in children 24 to 59 months of age, finally in infants 9 months of age. Infants will also receive a third vaccination. Three different doses of the vaccine \[low (Dose A), medium (Dose B), and high (Dose C) amounts of antigen\] will be evaluated using an age de-escalation approach (from least vulnerable adult population to most vulnerable paediatric population). The results of this study will allow the selection of the most appropriate dose for further vaccine development in infants 9 months of age, which is the main target age group for this vaccine.
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Anti-serotype specific Shigella lipopolysaccharide (LPS)/O-Antigen (OAg) serum immunoglobulin G (IgG) geometric mean concentrations (GMCs) in infants 9 months of age in Africa
Timeframe: At Day 281 (28 days after the third study intervention administration)
Number of adults 18 to 50 years of age in Europe with solicited administration site events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1 and Day 85/Day 169)
Number of adults 18 to 50 years of age in Europe with solicited systemic events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1 and Day 85/Day 169)
Number of adults 18 to 50 years of age in Europe with unsolicited adverse events (AEs)
Timeframe: During 28 days after each study intervention administration (study interventions administered at Day 1 and Day 85/Day 169)
Number of adults 18 to 50 years of age in Europe with serious adverse events (SAEs)
Timeframe: During the entire study participation period [Day 1 to Day 113 (for ST1_Adults_Placebo_GR1 and ST1_Adults_Dose C_GR1 groups)/Day 197 (for ST1_Adults_Placebo_GR2 and ST1_Adults_Dose C_GR2 groups)
Number of adults 18 to 50 years of age in Europe with deviations from normal values of haematological, renal, and hepatic panel test results at Day 8 (7 days after the first study intervention administration)
Timeframe: At Day 8 (7 days after the first study intervention administration)
Number of adults 18 to 50 years of age in Europe with deviations from normal values of haematological, renal, and hepatic panel test results at Day 92/Day 176 (7 days after the second study intervention administration)
Timeframe: At Day 92 (for ST1_Adults_Placebo_GR1 and ST1_Adults_Dose C_GR1 groups)/Day 176 (for ST1_Adults_Placebo_GR2 and ST1_Adults_Dose C_GR2 groups) (7 days after the second study intervention administration)
Number of adults 18 to 50 years of age in Africa with solicited administration site events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1 and Day 85)
Number of adults 18 to 50 years of age in Africa with solicited systemic events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1 and Day 85)
Number of adults 18 to 50 years of age in Africa with unsolicited AEs
Timeframe: During 28 days after each study intervention administration (study interventions administered at Day 1 and Day 85)
Number of adults 18 to 50 years of age in Africa with SAEs
Timeframe: During the entire study participation (Day 1 to Day 113)
Number of adults 18 to 50 years of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 8 (7 days after the first study intervention administration)
Timeframe: At Day 8 (7 days after the first study intervention administration)
Number of adults 18 to 50 years of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 92 (7 days after the second study intervention administration)
Timeframe: At Day 92 (7 days after the second study intervention administration)
Number of children 24 to 59 months of age in Africa with solicited administration site events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1 and Day 85)
Number of children 24 to 59 months of age in Africa with solicited systemic events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1 and Day 85)
Number of children 24 to 59 months of age in Africa with unsolicited AEs
Timeframe: During 28 days after each study intervention administration (study interventions administered on Day 1 and Day 85)
Number of children 24 to 59 months of age in Africa with SAEs
Timeframe: During the entire study participation period (Day 1 to Day 113)
Number of children 24 to 59 months of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 8 (7 days after the first study intervention administration)
Timeframe: At Day 8 (7 days after the first study intervention administration)
Number of children 24 to 59 months of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 92 (7 days after the second study intervention administration)
Timeframe: At Day 92 (7 days after the second study intervention administration)
Number of infants 9 months of age in Africa with solicited administration site events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1, Day 85 and Day 253)
Number of infants 9 months of age in Africa with solicited systemic events
Timeframe: During 7 days after each study intervention administration (study interventions administered at Day 1, Day 85 and Day 253)
Number of infants 9 months of age in Africa with unsolicited AEs
Timeframe: During 28 days after each study intervention administration (study intervention administered at Day 1, Day 85 and Day 253)
Number of infants 9 months of age in Africa with SAEs
Timeframe: During the entire study participation period (Day 1 to Day 281)
Number of infants 9 months of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 8 (7 days after the first study intervention administration)
Timeframe: At Day 8 (7 days after the first study intervention administration)
Number of infants 9 months of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 92 (7 days after the second study intervention administration)
Timeframe: At Day 92 (7 days after the second study intervention administration)
Number of infants 9 months of age in Africa with deviations from normal values of haematological, renal, and hepatic panel test results at Day 260 (7 days after the third study intervention administration)
Timeframe: At Day 260 (7 days after the third study intervention administration)