Antibody response to influenza vaccine in pediatric liver transplant recipients

Background: Data on the immunogenicity of the influenza vaccine in children after liver transplantation are sparse. Our study aims to evaluate the response of such patients to the trivalent influenza vaccine, administered by different protocols in 2 influenza seasons. Methods: Children attending the Liver Transplantation Unit of a tertiary care medical center were prospectively recruited and immunized with the inactivated subvirion influenza vaccine during the influenza seasons of 2004/2005 (1 dose, n = 18) and 2005/2006 (2 doses 4-6 weeks apart, n = 32). Antibodies were measured by hemagglutination inhibition assay. Immunity was defined as a titer of 1:40, and response was defined as a 4-fold increase in antibody titer from baseline. Results: In 2004/2005, the proportions of patients with protective antibodies were similar before and after 1 dose of vaccine. We found significant difference after the first dose for the A/H3N2 Wisconsin strain (43.2% vs. 70.3%, P = 0.003) and B/Malaysia strains (8.1% vs. 35.1%, P = 0.003) and for A/H1N1 New Caledonia strain (48.6% vs. 64.9% vs. 75%, P = 0.08, 0.005, respectively) after the second dose in 2005/2006 season. In 2004/2005, geometric mean titers rose significantly (P = 0.03) for the A/H3N2 New York strain; in 2005/2006, geometric mean titers for A/H3N2 New York and B/Malaysia increased after the first dose and for A/H1N1 New Caledonia after the second dose. Antibody titers were unrelated to age at transplantation, time from transplantation, and number of immunosuppressive drugs used. No serious vaccine-related events were documented. Conclusions: Liver-transplanted children respond to influenza vaccination. For some strains, the response is similar to that reported for healthy children. A second vaccine dose yielded no statistically significant benefit.