This is a Phase 2b randomized, double-blind, placebo-controlled vaccination and challenge study to assess the protective efficacy of the Vaxart Norovirus vaccine (VXA-G1.1-NN). Healthy adults will be randomized in a 1:1 ratio to receive one oral dose of vaccine or placebo. * Arm 1: VXA-G1.1-NN oral vaccine tablets \[1x1011 IU±0.5 log\] * Arm 2: Placebo tablets similar in appearance and number to active vaccine tablets Approximately 28 days post-vaccination, subjects will be admitted to an isolation ward and challenged with the NV GI.1 Norwalk challenge strain. After challenge, subjects will be monitored for signs and symptoms of acute gastroenteritis (AGE) from Day 29 to discharge. At 4 days post challenge (Day 33) asymptomatic subjects will be discharged from the isolation ward and will be followed in a series of outpatient visits and telephone calls. Symptomatic subjects may be kept in the isolation ward for up to an additional 3 days.
Study Population Healthy male and female adult volunteers age 18 to 49 years inclusive with blood type O or A and who are confirmed H type-1 antigen secretory positive Investigational Product Active Vaccine: * Norovirus GI.1 Norwalk VP1 Vaccine (VXA-G1.1-NN), an Oral E1/E3-Deleted Replication-Defective Recombinant Adenovirus serotype 5 with double-stranded ribonucleic acid (dsRNA) Adjuvant. The vaccine vector encodes for a full-length VP1 gene from Norwalk virus (NV). The adjuvant is a short hairpin RNA, expressed as a 21 nucleotide sequence (GAAACGA TATGGGCTGAATAC) as a tandem sequence in forward and reverse orientations separated by 6 nucleotides that comprise the loop of the RNA. The final drug product (DP) is formulated into enteric-coated tablet. * Dose: 1x10E11 IU±0.5 log Placebo Control: • Oral tablets similar in appearance and number to active vaccine tablets Multiple tablets of study drug will be dispensed to allow delivery of the intended vaccine dose (1x10E11 IU). A matching number of placebo tablets will be dispensed to maintain the study blinding. Viral Challenge Inoculum * Norovirus GI.1 (Norwalk Virus Inoculum Lot 001-09NV, IND 14697) * Dose: 1x10E6 Genomic Copies (GC). A dose which allows 50% - 65% infectivity in the healthy adult population (per NV infection rate observed in the GI.1 viral titration study Study Hypothesis Norovirus vaccine (VXA-G1.1-NN) will protect against Norovirus Gastroenteritis (NVG) related to norovirus (NoV) infection in the challenge model Approximately 120 subjects will be dosed in the vaccination phase to ensure at least 100 subjects (\~ 50 VXA-G1.1-NN vaccine and 50 placebo) are available to participate in the challenge phase. Approximately 28 days post-vaccination, subjects will be admitted to an isolation ward and challenged with the NV GI.1 Norwalk challenge strain. After challenge, subjects will be monitored for signs and symptoms of acute gastroenteritis (AGE) from Day 29 to discharge. NV illness lasts 2-4 days and is self-limited. At 4 days post challenge (Day 33) asymptomatic subjects will be discharged from the isolation ward and will be followed in a series of outpatient visits and telephone calls. Symptomatic subjects may be kept in the isolation ward for up to an additional 3 days. The following study visits and remote contacts will be conducted during the study Vaccination Phase: * Pre-Screening Period (Days -90 to Screening) may be utilized for purposes of ascertaining subjects' H type-1 antigen secretory status and blood type * Screening Period (Days -45 to -1) * Day 1 Visit (Baseline assessments; day of randomization and vaccination) * Day 8 Visit (safety and evaluation of immune response) * Day 28 (evaluation of immune response; 1 day prior to challenge, start inpatient stay) Challenge Phase: * Day 29 (viral challenge, sequestration) * Days 30 to 33 (sequestration - discharge; +3 days) * Day 36 Visit (evaluation of immune response and safety assessment) * Day 57 Visit (end of active period) Safety Follow-Up: * Day 120, Day 180, Day 240 and Day 300 (follow-up contact) * Day 185 (follow-up phone call): Study completion An independent Safety Monitoring Committee (SMC) will convene at pre-defined intervals during the norovirus challenge period, and also ad hoc as needed during the vaccination and challenge periods, to oversee the safety of the study.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
PREVENTION
Masking
SINGLE
Enrollment
165
Norovirus GI.1 Norwalk VP1 Vaccine, Oral E1-/E3-Deleted Replication Defective Recombinant Adenovirus 5 with dsRNA Adjuvant
Oral tablets similar in appearance and number to active vaccine tablets
Norwalk Virus Inoculum Lot 01-09NV
AltaSciences LA
Cypress, California, United States
Number of Participants Who Experienced Norovirus Gastroenteritis (NVG)
NVG is a composite endpoint defined as meeting both the definition of AGE and NV. AGE was defined as meeting any one of 3 criteria (diarrhea, vomiting, or diarrhea and vomiting) in any 24-hr rolling period. The individual criteria for diarrhea, vomiting, or diarrhea and vomiting were as follows: 1\. Diarrhea: i. ≥ 3 loose or liquid stools in any 24-hr rolling period, or ii. 400 g of loose or liquid stools in any 24-hr rolling period 2. Vomiting: ≥ 2 vomiting episodes in any 24-hr rolling period, or 3. Diarrhea and vomiting: i. one vomiting episode plus any loose or liquid stool in any 24-hr rolling period ii. one vomiting episode plus ≥ 2 of the following events in any 24-hr rolling period: 1. nausea 2. fever (oral temperature ≥ 37.6°C) 3. abdominal cramps or pains 4. abdominal gurgling or bloating 5. myalgia NV infection was defined as having 1 or more positive results in stool or urine by quantitative real time reverse transcription polymerase chain reaction (qRT-PCR).
Time frame: Up to approximately Day 57
Levels of Viral Protein 1, Major Capsid, or Surface Protein of Viruses (VP1)-Specific Immunoglobulin A (IgA) Antibody-Secreting Cell (ASC) Against Norwalk at Day 8
Blood samples were collected at different timepoints throughout the study.
Time frame: Day 8
Geometric Mean Titer (GMT) of Histo-blood Group Antigen (HBGA) Blocking Antibodies Against NV by Blocking Titer 50 (BT50) at Day 28
Blood samples were collected at different timepoints throughout the study. A positive change indicates an increase in titers.
Time frame: Day 28
VP1-specific Serum Immunoglobulin G (IgG) Response at Day 28
Blood samples were collected at different timepoints throughout the study.
Time frame: Day 28
VP1-specific Serum IgA at Day 28
Blood samples were collected at different timepoints throughout the study.
Time frame: Day 28
Number of Participants Who Experienced Solicited Symptoms of Reactogenicity
Solicited symptoms of reactogenicity included: * Gastrointestinal reactions: nausea, vomiting, diarrhea and abdominal pain * Systemic reactogenicity: malaise/fatigue, anorexia, fever, headache and myalgia
Time frame: Up to Day 8
Number of Participants Who Experienced Unsolicited Adverse Events (AEs) During the Vaccination Phase
Unsolicited AEs referred to any AEs that occurred during a clinical trial but were not specifically pre-defined or actively sought by the study protocol. Unsolicited AEs could include any medical condition or symptom, whether or not it was related to the intervention being studied.
Time frame: Up to Day 28 of Vaccination Phase (28-days phase)
Number of Participants Who Experienced Serious AEs (SAEs), AEs of Specific Interest (AESIs), and New Onsets of Chronic Illness (NOCIs)
A SAE was any AE that resulted in one or more of the following outcomes: death, a life-threatening event where the subject was at immediate risk of death (not hypothetically), inpatient hospitalization or the prolongation of existing hospitalization, persistent or significant incapacity or substantial disruption of normal life functions, congenital abnormality or birth defect, or an important medical event that, that jeopardized the participant's health or required medical or surgical intervention to prevent a serious outcome. A NOCI was defined as the diagnosis post-study drug administration of a new medical condition, which was chronic in nature, including those potentially controllable by medication (e.g., diabetes, asthma).
Time frame: Up to approximately 12 months post vaccination
Number of Participants Who Experienced Unsolicited AEs During the Challenge Phase
Unsolicited AEs referred to any AEs that occurred during a clinical trial but were not specifically pre-defined or actively sought by the study protocol. Unsolicited AEs could include any medical condition or symptom, whether or not it was related to the intervention being studied.
Time frame: Up to Day 29 of Challenge Phase (28-days phase)
Number of Participants With AGE During the Inpatient Challenge Phase
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AGE was defined as meeting any one of 3 criteria (diarrhea, vomiting, or diarrhea and vomiting) in any 24-hr rolling period. The individual criteria for diarrhea, vomiting, or diarrhea and vomiting were as follows: 1\. Diarrhea: i. ≥ 3 loose or liquid stools produced in any 24-hr rolling period, or ii. 400 g of loose or liquid stools produced in any 24-hr rolling period 2. Vomiting: ≥ 2 vomiting episodes in any 24-hr rolling period, or 3. Diarrhea and vomiting: i. one vomiting episode plus any loose or liquid stool in any 24-hr rolling period ii. one vomiting episode plus ≥ 2 of the following events in any 24-hr rolling period: 1. nausea 2. fever (oral temperature ≥ 37.6°C) 3. abdominal cramps or pains 4. abdominal gurgling or bloating 5. myalgia
Time frame: Day 28 of Challenge Phase (28-days phase)
Severity of AGE Assessed Using the Modified Vesikari Scale
The Modified Vesikari Scale is a tool used to assess the severity of AGE by evaluating symptoms such as diarrhea, vomiting, fever, and dehydration. It scores these symptoms based on their frequency and severity, with a minimum score of 0 and a maximum score of 20, where higher scores indicate more severe symptoms and lower scores suggest milder or no symptoms and severity.
Time frame: Up to approximately Day 36
Number of Participants Who Experienced Moderate or Severe Gastroenteritis
Moderate or severe gastroenteritis was defined by cumulative loose stools ≥ 1000gr during the inpatient period.
Time frame: Up to approximately Day 57
Duration of AGE
Time to onset of AGE was calculated as the time from challenge administration to the first recorded instance of an event satisfying the criteria for AGE. AGE was defined as meeting any of the 3 criteria: 1\. Diarrhea: i. ≥ 3 loose or liquid stools in any 24-hr rolling period, or ii. 400 g of loose or liquid stools in any 24-hr rolling period 2. Vomiting: ≥ 2 vomiting episodes in any 24-hr rolling period, or 3. Diarrhea and vomiting: i. one vomiting episode plus any loose or liquid stool in any 24-hr rolling period ii. one vomiting episode plus ≥ 2 of the following events in any 24-hr rolling period: 1. nausea 2. fever (oral temperature ≥ 37.6°C) 3. abdominal cramps or pains 4. abdominal gurgling or bloating 5. myalgia
Time frame: Up to approximately Day 57
Number of Participants Who Experienced Incidences of Diarrhea or Emesis
Classification of diarrhea was done through grading stools with Grade 3 (thick liquid stool) to Grade 5 (clear water diarrheal stool) being considered diarrhea.
Time frame: Up to approximately Day 57
Number of Participants With Norovirus (NoV) Infection up to Challenge Period Day 8
NoV infection was defined as a positive qRT-PCR in stool or emesis up to Challenge Period Day 8, and the presence of NV antigen in stool.
Time frame: Challenge Phase Day 8 (equal to Study Day 36)
Geometric Mean Genome Copies (GCs) of NoV Shedding in Stool Measured by qRT-PCR
NoV shedding was assessed by qRT-PCR. Stool samples were reported on 10\^3 copies/gm. If a participant produced multiple results for a given study day, the result with the largest shedding response was used for analysis. Samples that were reported as "Not Quantifiable" or as lower than the limit of detection (LOD) were analyzed as ½2\*LOD (76.2).
Time frame: Pre-challenge up to Day 8 of Challenge Phase (equal to Study Day 36)
Geometric Mean GCs of NoV Shedding in Emesis Measured by qRT-PCR
NoV shedding was assessed by qRT-PCR. Emesis samples were reported in 10\^3 copies/mL. If a participant produced multiple results for a given study day, the result with the largest shedding response was used for analysis. Samples that were reported as "Not Quantifiable" or as lower than the limit of detection (LOD) were analyzed as ½2\*LOD (15.3).
Time frame: Pre-challenge up to Day 8 of Challenge Phase (equal to Study Day 36)
Duration of NoV Infection
Duration of NoV Infection was defined as the time from NoV infection to the time of resolution of infection, defined as a negative qRT-PCR result not followed by a positive qRT-PCR result.
Time frame: Up to approximately Day 57