Influenza Virus Vaccine Plus Vitamin A and D Supplements for Prevention of Respiratory Virus Infections in Children

Participants will be randomized to receive either an influenza virus vaccine plus Vitamins A \& D or an influenza virus vaccine plus placebo. They will be stratified based on retinol binding protein (RBP) levels at screening, using a cut-off indicative of Vitamin A insufficiency (≤22,000 ng/ml). Co-enrolled sibling participants will be first stratified by RBP levels, then siblings within the same stratum will be equally assigned to different arms to provide greater assurance of balanced treatment assignment. Children will be tested for vitamin levels and immune responses before and after influenza virus vaccinations to determine if vitamin supplementation improves the influenza virus vaccine-induced antibody immune response. All participants will receive two doses of an influenza virus vaccination administered at least 28 days apart. Vitamin levels and antibody responses toward the vaccine will be measured on day 0 (baseline levels obtained where day 0 equals the first influenza virus vaccination administration), day 28, and day 56. Placebo or Vitamins A + D (at the levels of 20,000 IU and 2,000 IU, respectively) will be administered orally on the days of vaccination. Blood serum samples will be collected from participants on Day 0, prior to receiving influenza virus vaccine on Day 28, and during their Day 56 follow-up visit. Parents will be asked to fill out diary cards to indicate food intake for children during the study period along with an optional food frequency questionnaire given on day 56. Specific measurements on days 28, and 56 will include analyses of vaccine-specific and total IgA, IgG, and IgA/IgG plus IgA/IgM ratios in sera. Functional activities of antibodies toward influenza vaccine will also be measured.