Influenza vaccine antibody response and 6-month persistence in lung transplant recipients using two definitions of seroprotection.

Background: Lung transplant recipients are among those with the highest risk of influenza infection and complications each year. A few studies show adequate responses after influenza immunization; no studies examined the season-long protection.

Methods: Influenza antibody concentrations were measured using hemagglutination inhibition assays before immunization, 2 to 4 weeks after immunization, and 6 months after immunization in 25 healthy controls and 54 lung transplant patients. Two definitions of seroprotection (40 hemagglutination units (HAU) and 160 HAU which confers about 95% protection) were used.

Results: Influenza vaccine responses were high in both groups postimmunization (100% at 40 HAU and 60% healthy and 61% lung transplant at 160 HAU; P = 1.0; chi-square). At 6 months after immunization, seroprotection rates at 40 HAU (95% healthy and 97% lung transplant; P = 1.0) and at 160 HAU (24% healthy and 36% lung transplant; P = 0.40) were observed.

Conclusion: Seroprotection rates do not differ between healthy and transplant groups over 6 months when 40 HAU or 160 HAU is used. However, the seroprotection rates are disappointingly low when 160 HAU (the antibody concentration associated with 95% protection from infection) is used. Annual influenza vaccine should continue to be a high priority for lung transplant patients.