In the recent past, immunization policy-making bodies advised against immunizing too early in the influenza season because vaccine-specific antibody may wane before the end of the influenza season. This recommendation was based on only a small amount of data in frail elderly individuals, and further examination of the evidence shows that influenza vaccine antibody may last much longer. The influenza immunization timing recommendation is now changed to immunize when vaccine is available and continue throughout the season.~These changes led the investigators to the question of duration of influenza vaccine-induced antibody in lung transplant patients. No published studies of antibody persistence in this population could be found.~As part of a 5-year study of influenza antibody response in lung transplant patients, in patients awaiting lung transplantation, and in healthy controls, serum was obtained before and 2-4 weeks after influenza immunization for each season. Therefore, a serum sample was collected on each participant approximately 11 months after influenza vaccine administration for each of 4 years.~To investigate duration of influenza antibody titers, antibody concentrations to the previous season's vaccine antigens were measured.~The hypothesis is that immunosuppressed lung transplant patients would maintain protective concentrations of influenza antigen-specific antibodies (an antibody titer of at least 1:40) beyond the influenza season.~[This substudy that was originally registered to NCT00205270 and subsequently registered to its own NCT number for the purpose of clarity in linked results]
This a sub-study of a 5-year study designed to investigate how antibody and T cell responses following influenza vaccine compare among lung transplant patients, patients waiting for lung transplantation, and healthy individuals.~This study is designed to investigate influenza vaccine-induced antibodies in lung transplant patients between seasons.