The final models for predicting influenza H1 and H3 IgA antibody response at Day 28, based on the bacterial taxa on Day 28, included B. ovatus presence on Day 28 post-immunization, which was associated with an increase in both H1-specific IgA antibody titers (coefficient = 0.042) and H3-specific IgA antibody titers (coefficient = 0.074). This evidence concerns the gene CD79A and influenza.