We explored the potential for a biphasic pattern in waning of antibody titers after influenza vaccination. We collected blood samples in a randomized controlled trial of influenza vaccination in children, and tested them with hemagglutination inhibition (HAI) assays for influenza A(H3N2) and influenza B/Victoria lineage. Using piecewise log-linear mixed-effect models, we found evidence for a faster initial waning of antibody titers for the first 1-2 years after vaccination and then slower longer-term declines. Children with higher post-vaccination titers had faster antibody decay.