This trial in healthy adults will determine the effects of beta-glucan, a dietary fiber supplement isolated from baker's yeast, on immune response to the influenza vaccine.

Beta-glucans have been shown to enhance the innate and adaptive immune responses in cell cultures, animal models, and humans, thus adults over the age of 50 years receiving the influenza vaccination may benefit in terms of their immune response from supplementation with beta-glucans. This is a 6-week randomized, double-blind, placebo-controlled, 2-arm parallel study designed to evaluate the adjuvant effect of beta-glucan dietary supplementation during influenza vaccination. Participants will consume either the beta-glucan or placebo capsules for 42 days. Participants will complete an online Qualtrics daily questionnaire of compliance, fatigue, and cold and flu symptoms throughout the 42-day study. Influenza vaccine will be administered on or about day 14. The Gastrointestinal Symptom Rating Scale (GSRS) and the Mood and Feelings Questionnaire (MFQ) will be completed at baseline, 2 weeks and 6 weeks. Blood draws for antibody and cytokine response will be completed at baseline, and on or about days 14 and 15, and on day 42.

Inclusion Criteria:

1. Adult volunteers ≥ 50 years of age.
2. Planning to be vaccinated for influenza
3. Have been immunized for COVID-19
4. Willing and able to provide written informed consent in English.
5. Willing and able to comply with all the study-related procedures, including attending to study visits for blood draw, taking the influenza vaccine, intake of the study supplement, and completing study questionnaires.

Exclusion Criteria:

1. Demonstrate an inability to comply with the study-related procedures.
2. Have a history of a severe reaction or hypersensitivity following vaccination with influenza vaccine, vaccination with any other vaccine containing the same substances, or intake of the study product.
3. Have an immune system alteration because of an underlying illness (e.g., autoimmune disease) or immune-suppressing treatment (e.g., steroids (last 30 days); cytotoxic drugs, medical surgery, or radiation therapy during the 6 months, previous to enrollment).
4. Be concurrently participating in a clinical trial that, in the judgement of the investigator, would interfere with the evaluation of the study outcomes.

42 days