Persistence of Influenza Vaccine-induced Antibody in Lung Transplant Patients and Healthy Individuals Beyond the Season

Every year influenza infection causes significant morbidity and mortality in the general population making it a serious public health concern. Among those at highest risk for complications from infection are the immunocompromised. Effective influenza immunization that confers protection throughout the season is critical for lung transplant recipients because in addition to aggressive immunosuppressive therapy, infection directly affects the transplanted organ. Studies of influenza vaccine response rates in lung transplant patients show generally lower antibody concentrations, but acceptable influenza vaccine response rates compared with healthy individuals. However, little is known about the persistence of influenza vaccine-induced antibody concentration in either healthy or immunosuppressed populations.

Influenza antibody concentrations persist at seroprotective levels (defined as antibody concentrations at least 40 hemagglutination units) up to a year post vaccination. However, the investigators could find no information regarding persistence beyond one year.

It is hypothesized that the high rates of persisting influenza vaccine antibody in immunosuppressed lung transplant individuals would match the rates of persisting vaccine-antibody in healthy individuals.

Influenza antibody concentrations against viruses no longer included in the vaccine were measured in serum by hemagglutination inhibition assay (HIA) annually (individual participants followed for 3 years). Samples were collected at 2-4 weeks post-vaccination. Seroprotection was defined as a titer of ≥ 1:40 and was compared between groups over the measured term using Fisher's exact tests.

[This substudy that was originally registered to NCT00205270 and subsequently registered to its own NCT number for the purpose of clarity in linked results]