A Study to Evaluate Vaxart's Oral Bivalent GI.1/GII.4 Norovirus Vaccine in Healthy Lactating Females and Their Nursing Infants

Inclusion Criteria

• Lactating females aged ≥ 18 years at the time of enrolment and their breastfed infants aged >30 days to 11 months of age at the time of the participants' study drug administration.
• In stable and good general health, without significant medical illness, based on medical history, physical examination (including vital signs), and clinical judgment of the investigator.
• Lactating females willing and able to provide informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the protocol.
• Lactating females who are willing to provide consent for their breastfed infant.
• Negative pregnancy tests at screening and prior to dose on Day 1.
• Available for all planned visits and tele-health appointments, and ability to comply with all study-related evaluations (including but not limited to having the ability and willingness to swallow multiple small enteric-coated tablets per study dose, express/pump breastmilk, and collect infant stool samples).
• Plan to continue breastfeeding as the main source of the infant's nutrition for at least 1 month (longer is preferred with goal of 6 months post dose if possible) from the time of study drug administration. Exclusive breastfeeding is acceptable but not necessary.
• The nursing infant is the product of a singleton pregnancy AND does not have any of the following:
• Any abnormality that may interfere with breastfeeding or milk absorption
• Active infection (may be included if the infection resolves and the participant is re-assessed during the screening period)
• Infant has any other medical condition or abnormality that, in the opinion of the investigator, could compromise the infant's appropriate inclusion in this study including interference with the interpretation of study results (such as malabsorption)
• One or more documented brief resolved unexplained events (BRUEs)
• Extreme prematurity (infants who were born at less than 28 weeks gestation)
• 30 days of age or less at the participant's study drug administration OR greater than 11 months of age at the participant's study drug administration
• Prior hospitalization that is not exclusively for hyperbilirubinemia requiring phototherapy
• Any genetic/metabolic disease
• Any chronic illness requiring long term medication
• Participants must be willing to use a highly effective form of contraception for 30 days prior to vaccination and until 60 days after the vaccination. Acceptable forms are oral, implantable, intrauterine, transdermal, intravaginal, injectable, double barrier or abstinence (participants using diaphragms must also use condom). The form of contraception must be approved by the investigator.

Exclusion Criteria

• Presence of a fever ≥ 38.0°C measured orally at baseline, on Day 1 prior to vaccination. (Assessment may be repeated once during screening period).
• Acute disease within 72 hours prior to vaccination, defined as the presence of a moderate or severe illness (as determined by the Investigator through medical history and physical exam). (Assessment may be repeated once during screening period).
• Participants who have received antipyretic/analgesic medications within 24 hours prior to the intended vaccine administration.
• Positive human immunodeficiency virus (HIV), Hepatitis B surface antigen (HBsAg), or hepatitis C virus (HCV) tests at the screening visit.
• History of hypersensitivity or allergic reaction to any component of the investigational vaccine, including but not limited to fish gelatin.
• History of serious reactions to vaccination such as anaphylaxis, respiratory problems, hives, or abdominal pain.
• Presence of significant uncontrolled medical or psychiatric illness (acute or chronic) including the institution of new medical/surgical treatment or significant dose alteration for uncontrolled symptoms or drug toxicity within 3 months of screening and reconfirmed at baseline.
• Hist