Given the significant risk of morbidity and mortality, it is critical and highly recommended that lung transplant patients receive annual influenza immunizations that confer protection throughout the influenza season. Previous studies have demonstrated that transplant recipients and nonimmunocompromised populations display similar rates of seroprotection between 3 and 5 weeks after influenza vaccination, despite the transplant population achieving generally lower antibody concentrations. Two studies show influenza vaccine antibody persistence at reasonable rates at 1 year, but not 2 years, after immunization. However, there are no studies comparing seroprotection rates 6 months after vaccination, reflecting adequate coverage throughout the entire influenza season.~Seroprotection has traditionally been defined as an antibody concentration of at least 40 hemagglutination units (HAU) after vaccination, which is the criterion for influenza vaccine licensure. This concentration of antibody provides protection from infection at a rate of about 50% in typically healthy individuals. Protection from infection improves with higher antibody concentrations. For this study, a HAU of at least 160 was selected as a more conservative definition of seroprotection, where protection may reach up to 95%.~The hypothesis is that seroprotection, defined as 40 HAU or greater, will persist up to 6 months at high rates in lung transplant patients and that these rates will be comparable to the rates in healthy individuals. As a secondary outcome, seroprotection rates are compared when 160 HAU or greater was used to define seroprotection.~Influenza vaccine responses in lung transplant patients and healthy control subjects without lung disease will be compared over the course of the 2008 to 2009 influenza season.~Serum collected from participants before immunization, 2 to 4 weeks after immunization (postimmunization), and 6 months after immunization.~[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 two different definitions of influenza vaccine seroprotection at mid-season in lung transplant patients.